Rangefinders and aiming methods using projectile grouping

Abstract

A method for aiming a projectile weapon involves identifying a projectile group corresponding to a selected projectile and its nominal initial velocity from at least two different predetermined groups of projectiles, determining a range to a target, and automatically determining an aiming adjustment for aiming the projectile weapon based on the range to the target and a nominal ballistic characteristic of the projectile group. The nominal ballistic characteristic of the projectile group may be characteristic of a ballistic coefficient of the selected projectile and the nominal initial velocity of the selected projectile. Also disclosed are systems and methods for determining hold over aiming data and equivalent horizontal range data, for aiming projectile weapons at inclined targets.

Description

TECHNICAL FIELD

The field of this disclosure relates to methods and systems for compensating for ballistic drop and to rangefinders implementing such methods.

BACKGROUND

Exterior ballistic software is widely known and used for accurately predicting the trajectory of a bullet, including ballistic drop and other ballistic phenomena. Popular software titles include Infinity 5™, published by Sierra Bullets, and PRODAS™, published by Arrow Tech Associates, Inc. Many other ballistics software programs also exist. Ballistics software may include a library of ballistic coefficients and typical muzzle velocities for a variety of particular cartridges, from which a user can select as inputs to ballistic calculations performed by the software. Ballistics software typically also allows a user to input firing conditions, such as the angle of inclination of a line of sight to a target, range to the target, and environmental conditions, including meteorological conditions. Based on user input, ballistics software may then calculate bullet drop, bullet path, or some other trajectory parameter. Some such software can also calculate a recommended aiming adjustment that would need to be made in order to hit the target. Aiming adjustments may include holdover and holdunder adjustments (also referred to as come-up and come-down adjustments), designated in inches or centimeters at the observed range. Another way to designate aiming adjustment is in terms of elevation adjustment to a riflescope or other aiming device (relative to the weapon on which the aiming device is mounted), typically expressed in minutes of angle (MOA). Most riflescopes include adjustment knob mechanisms that facilitate elevation adjustments in ¼ MOA or ½ MOA increments.

For hunters, military snipers, SWAT teams, and others, it is impractical to carry a personal computer, such as a laptop computer, for running ballistics software. Consequently, some shooters use printed ballistics tables to estimate the amount of elevation adjustment necessary. However, ballistics tables also have significant limitations. They are typically only available for level-fire scenarios in ideal conditions or for a very limited range of conditions and, therefore, do not provide an easy way to determine the appropriate adjustments for aiming at inclined targets, which are elevated or depressed relative to the shooter.

Methods have been devised for using level-fire ballistics tables in the field to calculate an estimated elevation adjustment necessary for inclined shooting. The most well known of these methods is the so-called “rifleman's rule,” which states that bullet drop or bullet path at an inclined range can be estimated as the bullet path or bullet drop at the corresponding horizontal range to the elevated target (i.e., the inclined range times the cosine of the angle of inclination). However, the rifleman's rule is not highly accurate for all shooting conditions. The rifleman's rule and other methods for estimating elevation adjustment for inclined shooting are described in the paper by William T. McDonald titled “Incline Fire” (June 2003).

Some ballistic software programs have been adapted to operate on a handheld computer. For example, U.S. Pat. No. 6,516,699 of Sammut et al. describes a personal digital assistant (PDA) running an external ballistics software program. Numerous user inputs of various kinds are required to obtain useful calculations from the software of Sammut et al. '699. When utilizing ballistic compensation parameters calculated by the PDA, such as holdover or come-up, a shooter may need to adjust an elevation setting by manually manipulating an elevation adjustment knob of the riflescope. Alternatively, the user may need to be skilled at holdover compensation using a riflescope with a special reticle described by Sammut et al. '669. Such adjustments may be time consuming and prone to human error. For hunters, the delay involved in making such adjustments can mean the difference between making a shot and missing an opportunity to shoot a game animal.

The present inventors have identified a need for improved methods and systems for ballistic compensation that are particularly useful for inclined shooting and which would also be useful for archers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram level-fire and inclined-fire trajectories for a projectile;

FIG. 2 is a schematic diagram illustrating measurements and factors in calculating an equivalent horizontal range (EHR);

FIG. 3 is a flow chart showing method steps in accordance with an embodiment;

FIG. 4 is a computation flow diagram for solving EHR for bullets;

FIG. 5 is a computation flow diagram for solving EHR for arrows;

FIG. 6 is a pictorial view of a rangefinder according to an embodiment of a system for range measurement and ballistic calculations;

FIG. 7 is an enlarged view of an electronic display as viewed through an eyepiece of the rangefinder;

FIG. 8 is an elevation view of the display of FIG. 7 showing detail of displaying of calculated and measured data;

FIG. 9 is schematic block diagram of the riflescope of FIG. 6;

FIG. 10 is a pictorial view showing detail of an alternative targeting reticle and information display for a rangefinder;

FIG. 11 is a pictorial view of the targeting reticle and information display of FIG. 10, illustrating the graphical display of a recommended holdover aiming adjustment;

FIG. 12 is a side elevation view of a gun and riflescope; and

FIG. 13 is an enlarged pictorial view showing detail of a ballistic reticle of the riflescope of FIG. 12.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is a schematic diagram illustrating the effect on a projectile's trajectory of the inclination of the line along which projectile is fired, cast, or otherwise shot (the “line of initial trajectory” or, in the case of guns, the “bore line”). For purposes of illustration, the trajectory curves and angles between various lines in FIG. 1 are greatly exaggerated and not to scale.

With reference to FIG. 1, a “level fire” trajectory is the path along which a projectile moves when shot at a target T at range R₀ and at substantially the same geographic elevation as a vantage point VP of the shooter. The projectile weapon has a line of initial trajectory (“level fire bore line”) that is not actually level, but rather is inclined relative to the level fire line of sight (level fire LOS) by an elevation angle α. The level fire line of sight, which is approximately horizontal, begins at a height h above the beginning of the bore line. The height h and elevation angle α represent the typical mounting arrangement of a riflescope on a firearm or an archery sight on a bow. The level fire trajectory intersects the level fire line of sight at range R₀ which is known as the “sighted-in range” or “zero range” or “zeroed-in range” of the weapon and sight combination. The sighted-in range R₀ is typically established by shooting the weapon at a target at a known horizontal reference distance, such as 100 yards, and adjusting the elevation angle α of the riflescope or other sighting device until projectiles shot by the weapon impact the target at a point that coincides with the cross hairs or other aiming mark of the riflescope or other sighting device.

An “inclined fire trajectory” is also depicted in FIG. 1. The inclined fire trajectory represents the path along which the same projectile travels when aimed at a target that is elevated relative to vantage point VP. The height h and elevation angle α of the inclined fire line of sight relative to the bore line are the same as in the level-fire scenario. However, the inclined fire line of sight is inclined by angle of inclination θ. As illustrated in FIG. 1, the inclined fire trajectory crosses the inclined fire line of sight at a distance substantially greater than the sighted-in range R₀. This overshoot is due to the effect of gravity, which always acts in the vertically downward direction, regardless of the angle of inclination θ. The overshoot phenomena and prior methods of correcting for it are discussed in detail by William T. McDonald in his paper titled “Inclined Fire” (June 2003). The present inventors have observed that effects of inclination are typically even more pronounced in archery than for bullets, due to differences in the initial speed and aerodynamic characteristics of the projectiles used.

In accordance with embodiments described herein, it has been recognized that many hunters (including bow hunters) and other shooters, such as military law enforcement snipers, are versed in holdover techniques for compensating for ballistic drop in horizontal fire scenarios. A holdover adjustment involves aiming high by a measured or estimated amount. For example, a hunter shooting a deer rifle with a riflescope sighted in at 200 yards may know that a kill-shot for a deer (in the deer's heart) at a level-fire range of approximately 375 yards involves aiming the riflescope's cross hairs at the top of the deer's shoulders. Holdover adjustments are much faster in practice than elevation adjustments, which involve manually adjusting an elevation setting of the riflescope or other aiming device to change the elevation angle α of the aiming device relative to the weapon. They are also the primary mode of aiming adjustment for most archers. Holdover and holdunder techniques also avoid the need to re-zero the aiming device after making a temporary elevation adjustment.

Many varieties of ballistic reticles are employed in riflescopes to facilitate holdover and holdunder. For archery, a common ballistic aiming sight known as a pin sight is often employed for holdover aiming adjustment. Ballistic reticles and other ballistic aiming sights generally include multiple aiming marks spaced apart along a vertical axis. Exemplary ballistic reticles include mil-dot reticles and variations, such as the LEUPOLD TACTICAL MILLING RETICLE™ (TMR™) sold by Leupold & Stevens, Inc., the assignee of the present application; Leupold® DUPLEX™ reticles; the LEUPOLD SPECIAL PURPOSE RETICLE™ (SPR™); and LEUPOLD BALLISTIC AIMING SYSTEM™ (BAS™) reticles, such as the LEUPOLD BOONE & CROCKETT BIG GAME RETICLE™ and the LEUPOLD VARMINT HUNTER'S RETICLE™. BAS reticles and methods of using them are described in U.S. patent application Ser. No. 10/933,856, filed Sep. 3, 2004, titled “Ballistic Reticle for Projectile Weapon Aiming Systems and Method of Aiming” (“the '856 application”), which is incorporated herein by reference. As described in the '856 application, BAS reticles include secondary aiming marks that are spaced at progressively increasing distances below a primary aiming mark and positioned to compensate for ballistic drop at preselected regular incremental ranges for a group of ammunition having similar ballistic characteristics.

Equivalent Horizontal Range and Inclined Shooting Methods

In accordance with one embodiment depicted in FIGS. 2 and 3, a method 10 of inclined shooting involves the calculation of an equivalent horizontal range (EHR) that may be used by the shooter to make a holdover or elevation adjustment for accurately aiming a projectile weapon at an elevated or depressed target located at a inclined line of sight (LOS) range that is different from the EHR. With reference to FIG. 2, a shooter at vantage point VP determines a line-of-sight range to a target. As in FIG. 1, a zero range R₀ represents the horizontal-fire distance at which the projectile weapon and aiming device are sighted-in. Line-of-sight ranges R₁ and R₂ to two different targets are depicted in FIG. 2, illustrating the usefulness of the method with respect to both positive and negative ballistic path heights BP₁ and BP₂ relative to the inclined fire LOS. For purposes of illustration, the steps of method 10 (FIG. 3) will be described with reference to a generic LOS range R to a target T, shown in FIG. 2 at range R₂. However, skilled persons will appreciate that the methods described herein are equally applicable to “near” LOS ranges R₁ at which the ballistic path height BP₁ is positive, as well as to “far” LOS ranges R₂ at which the ballistic path height BP₂ is negative. The LOS range R may be determined by a relatively accurate ranging technique, such as a lidar (laser ranging) or radar, or by a method of range estimation, such as optical range estimating methods in which a distant target of known size is bracketed in a scale of an optical device, as described in the '856 application at paragraphs [0038] and [0049] thereof.

Methods 10 in accordance with the present disclosure also involve determining an inclination θ of the inclined LOS between vantage point VP and the target T. The angle of inclination θ may be determined by an electronic inclinometer, calibrated tilt sensor circuit, or other similar device. For accuracy, ease of use, and speed, an electronic inclinometer for determining the angle of inclination θ may be mounted in a common housing with a handheld laser rangefinder 50 of the kind described below with reference to FIGS. 6-9.

FIG. 3 is a flow diagram depicting steps of inclined shooting method 10, including the initial steps of determining the LOS range R (step 12) and determining the inclination θ of the inclined LOS (step 14). With reference to FIG. 3, after LOS range R and inclination θ have been determined (steps 12 and 14), the method 10 may involve a check (step 16) to determine whether the absolute inclination |θ| is less than a predetermined limit under which the effects of inclination can be disregarded and the LOS range R can be regarded as the equivalent horizontal range (EHR) (step 18).

Archery ballistics exhibit a more significant difference between positive and negative lines of initial trajectory (uphill and downhill shots) since the initial velocity is relatively low, giving the effects of gravity more time to affect the trajectory than with bullets, which reach their targets much faster. Especially at long ranges, uphill shots experience more drop than downhill shots; therefore, when applying the method 10 for archery, the check 16 may involve comparing a positive inclination θ against a positive limit and a negative inclination θ against a negative limit that is different from the positive limit. Mathematically, such a check would be expressed as:{lower_limit}≧θ≦{upper_limit}?

If the result of check 16 is negative, then a predicted trajectory parameter TP is calculated or otherwise determined at the LOS range for a preselected projectile P shot from vantage point VP toward the target T (step 20). Trajectory parameter TP may comprise any of a variety of trajectory characteristics or other characteristics of a projectile calculable using ballistics software. For example, trajectory parameter TP at LOS range R may comprise one or more of ballistic path height (e.g., arrow path or bullet path), ballistic drop relative to line of initial trajectory (e.g., the bore line in FIG. 1), observed ballistic drop perpendicular to LOS (i.e., vertical ballistic drop×cos(θ+α)), velocity, energy, and momentum. In accordance with the embodiment described below with reference to FIGS. 2 and 4, for R=R₂, trajectory parameter TP may comprise ballistic path BP₂ (e.g., bullet path). In another embodiment, described below with reference to FIG. 5, the trajectory parameter of ballistic path comprises arrow path (AP). However, nothing in the figures or written description should be construed as limiting the scope of possible trajectory parameters to only ballistic path.

After the trajectory parameter TP has been calculated, the method may then output the trajectory parameter TP (step 21) or calculate EHR based on the trajectory parameter TP or parameters (step 22). At step 21, the trajectory parameter TP output may comprise ballistic path height BP expressed as a linear distance in inches or millimeters (mm) of apparent drop, or as a corresponding angle subtended by the ballistic path height (e.g., BP₂ in FIG. 2) in minutes of angle (MOA) or milliradians (mils). The TP output (step 21) may comprise a display of numerical ballistic path data in an electronic display device, such as a display 70 of rangefinder 50 (FIG. 7) or a reticle 210 of riflescope 200 (FIGS. 10-12), as further described below. The TP output (step 21) may also comprise graphical display of a holdover aiming recommendation in a rangefinder display (FIGS. 10-11), a riflescope reticle (FIGS. 12-13), an archery sight, or another aiming sight, based on the trajectory parameter of ballistic path BP.

In one method of calculating EHR, a reference ballistics equation for a level-fire scenario (θ=0) comprising a polynomial series is reverted (i.e., through series reversion) to solve for EHR based on a previously calculated ballistic path height BP (e.g., BP₂). As depicted in FIG. 2, BP₂ corresponds to EHR₂ under level-fire conditions. Thus, EHR is calculated as the range at which trajectory parameter TP would occur if shooting projectile P in a level-fire condition from the vantage point VP toward a theoretical target T_th in a common horizontal plane with vantage point VP, wherein the horizontal plane coincides with the level fire LOS. Of course, the reference ballistics equation may be established to deviate slightly from horizontal without appreciable error. Consequently, the terms “horizontal”, “level fire LOS”, and other similar terms are preferably construed to allow for equations to deviate from perfect horizontal unless the context indicates otherwise. For example, when solving for EHR, the degree of levelness of the reference equations should facilitate calculation EHR with sufficient accuracy to allow aiming adjustments for inclined shooting resulting in better than ±6 inches of error at 500 yards throughout the range of between −60 and 60 degrees inclination. Ballistic trajectories are generally flatter at steeper shooting angles and trajectories of different projectiles are therefore more similar. Consequently, the deviation tends to be less significant at very steep inclines.

The calculation of trajectory parameter TP, the calculation of equivalent horizontal range EHR, or both, may also be based on a ballistic coefficient of the projectile P and one or more shooting conditions. The ballistic coefficient and shooting conditions may be specified by a user or automatically determined at step 24. Automatically-determined shooting conditions may include meteorological conditions such as temperature, relative humidity, and barometric pressure, which may be measured by micro-sensors in communication with a computer processor for operating method 10. Meteorological conditions may also be determined by receiving local weather data via radio transmission signal, received by an antenna and receiver in association with the computer processor. Similarly, geospatial shooting conditions such as the compass heading of the LOS to the target and the geographic location of the vantage point VP (including latitude, longitude, altitude, or all three) may be determined automatically by a GPS receiver and an electronic compass sensor in communication with the computer processor, to ballistically compensate for the Coriolis effect (caused by the rotation of the Earth). Alternatively, such meteorological and geospatial shooting conditions may be specified by a user and input into a memory associated with the computer processor, based on observations made by the user.

User selection of shooting conditions and ballistic coefficient may also involve preselecting or otherwise inputting non-meteorological and non-geospatial conditions for storage in a memory associated with a computer processor on which method 10 is executed. The ballistic coefficient and certain shooting conditions, such as the initial velocity of projectile P (e.g., muzzle velocity, in the case of bullets), may be set by a user simply by selecting from two or more weapon types (such as guns and bows), and from two or more ballistic groupings and possibly three, four, five, six, seven or more groups, wherein each group has a nominal ballistic characteristic representative of different sets of projectiles having similar ballistic properties. The sets (groups) may be mutually-exclusive or overlapping (intersecting). A sighted-in range of a weapon aiming device and a height of the weapon aiming device above a bore line of a weapon may also be entered in this manner. In a rangefinder device 50 for operating the method, described below with reference to FIGS. 6 and 7, the weapon type and ballistic group may be selected from a menu of possible choices during a menu mode or setup mode of rangefinder device 50.

After a trajectory parameter TP has been calculated at step 20 or EHR has been calculated at step 22, method 10 then involves outputting TP or EHR in some form (step 21 or 26). For example, TP or EHR may be displayed via a display device, such as an LCD display, in the form of a numeric value specified in a convenient unit of measure. For example, TP output may be expressed as ballistic path height BP in inches or mm of apparent drop or as an angle (in MOA or mils) subtended by the ballistic path height BP. EHR may be expressed in yards or meters, for example. In other embodiments, BP or EHR may be effectively output via a graphical representation of the data, through the identification of a reticle aiming mark corresponding to the BP or EHR, for example, as described below with reference to FIGS. 10-13.

Once the EHR is output 26, it can then be employed to aim the projectile weapon (step 28) at target T along the inclined LOS at R₂. In one embodiment, a shooter merely makes a holdover or holdunder adjustment based on the calculated EHR, as if she were shooting under level-fire conditions—it being noted that wind effects, firearm inaccuracy, and shooter's wiggle are still in effect over the entire LOS range R₂. In another embodiment, the shooter adjusts an elevation adjustment mechanism of a riflescope or other aiming device based on the displayed EHR. Similar elevation adjustments may be made based on the display of the calculated trajectory parameter TP (step 21).

Ballistic Calculation Methods

FIG. 4 summarizes details of one possible sequence of steps for calculating a trajectory parameter of bullet path (BP) and equivalent horizontal range (EHR) for bullets. The calculation sequence 30 begins with selection of a ballistic group (A, B, or C) in which the bullet and cartridge are listed (step 31). Ballistic grouping may effectively normalize groups of bullets having similar characteristics, based on their ballistic coefficients, muzzle velocities and masses. Listings of cartridges in the various groupings may be provided to the user by a printed table or software-generated information display, facilitating selection of the appropriate ballistic group. Reference trajectories for ballistic groups A, B, and C are set forth in TABLE 3, below. The other inputs to the calculations include the LOS range R and the inclination angle θ, which may be determined automatically by a handheld laser rangefinder with inclinometer (step 32). The calculation method involves solving the following polynomial equation for bullet path:BP=a₀+a₁R+a₂R²+a₃R³+ . . .(step 36), wherein the coefficients a₀, a₁, a₂, etc. are calculated from the inclination angle θ based on a series of polynomial equations 34 in which the coefficients thereof (identified in FIG. 4 as A₀₀, A₀₁, A₀₂, etc.) are different stored parameters for each ballistic group A, B, and C. A single equation 36 is suitable for both positive and negative angles of inclination, expressed as absolute angular values. After bullet path BP has been determined, the BP is then used as an input to one of two different reversions of the bullet path equation for θ=0 to solve for EHR. If bullet path BP is positive (test 38), then a “short-range EHR” polynomial equation is used (step 40), wherein B₀, B₁, . . . , B₆ are parameters corresponding to the selected ballistic group. If BP is negative (test 38), then a “long-range EHR” polynomial equation is used (step 42), wherein C₀, C₁, . . . , C₆ are parameters corresponding to the selected ballistic group. Each ballistic group also has an associated coefficient named BPLIM, which is an upper limit for BP in the computations shown in FIG. 4. Parameters A₀₀ to A₄₃, B₀ to B₆, and C₀ to C₆ are constants that are stored for each of the ballistic groups and recalled based on the selected ballistic group for purposes completing the calculations 30.

FIG. 5 illustrates a similar sequence of calculations 30′ for archery. In FIG. 5 reference numerals 31′, 32′, 36′, etc. indicate steps that correspond to respective steps 31, 32, 36, etc. of FIG. 4. However, unlike the calculations for bullets 30 (FIG. 4), the calculation of ballistic path for arrows 30′ (hereinafter arrow path AP) must take into account whether the inclination angle is positive or negative (branch 33′), due to the increased flight time of arrows and attendant increased effects of gravity on their trajectory. For this reason, the calculations involve one of two different sets of coefficients A_ij and D_ij, (for i=1, 2, 3, 4, 5 and j=1, 2, 3, 4, 5) depending on whether the inclination is positive (step 34a′) or negative (step 34b′). Parameters A₀₀ to A₄₃, B₀ to B₆, C₀ to C₆, D₀₀ to D₄₃, APLIM, and EHRLIM are constants that are stored in memory for each of the ballistic groups and recalled based on the selected ballistic group for purposes completing the calculations 30′.

Table 2 lists one example of criteria for ballistic grouping of bullets and arrows:

TABLE 2
Ballistic group Characteristic ballistic drop (without incline)
Arrow group A   Arrow drop of 20 to 30 inches from the 20-yard sight pin
                at 40 yards
Arrow group B   Arrow drop of 30 to 40 inches from the 20-yard sight pin
                at 40 yards
Arrow group C   Arrow drop of 10 to 20 inches from the 20-yard sight pin
                at 40 yards
Bullet group A  Rifles sighted in at 200 yards with 30 to 40 inches drop
                at 500 yards
Bullet group B  Rifles sighted in at 200 yards with 40 to 50 inches drop
                at 500 yards
Bullet group C  Rifles sighted in at 300 yards with 20 to 30 inches drop
                at 500 yards

Arrow groupings may be more dependent on the launch velocity achieved than the actual arrow used, whereas bullet groupings may be primarily based on the type of cartridge and load used. Table 3 lists example reference trajectories from which the calculation coefficients of FIG. 4 may be determined for ballistic groups A, B, and C.

TABLE 3
A Winchester Short Magnum with Winchester 180 grain Ballistic
  Silvertip bullet at 3010 fps, having a level fire bullet
  path of −25.21 inches at 500 yards.
B 7 mm Remington Magnum with Federal 150 grain SBT GameKing
  bullet at 3110 fps, having a level fire Bullet Path of −34.82
  inches at 500 yards.
C 7 mm-08 Remington with Remington Pointed Soft Point Core-
  Lokt bullet at 2890 fps, having a level fire Bullet Path
  of −45.22 inches at 500 yards.

Alternatives to solving a series of polynomial equations also exist, although many of them will not provide the same accuracy as solving a polynomial series. For example, a single simplified equation for ballistic drop or ballistic path may be used to calculate a predicted trajectory parameter, and then a second simplified equation used to calculate EHR from the predicted trajectory parameter. Another alternative method of calculating EHR involves the “Sierra Approach” described in William T. McDonald, “Inclined Fire” (June 2003), incorporated herein by reference. Still another alternative involves a table lookup of a predicted trajectory parameter and/or interpolation of table lookup results, followed by calculation of EHR using the formula identified in FIG. 4. Yet another alternative involves determining both the predicted trajectory parameter and EHR by table lookup and interpolation, using stored sets of inclined-shooting data at various angles.

Example

The following table (TABLE 1) illustrates an example of an EHR calculation and compares the results of aiming using EHR to aiming with no compensation for incline, and aiming by utilizing the horizontal distance to the target (rifleman's rule).

TABLE 1
	.300 WSM, 165 grain Nosler Partition,
Load	3050 fps muzzle velocity
Angle of inclination	50°
Inclined line-of-sight range	500	Yards
Equivalent Horizontal Range	389	Yards
(EHR)
Ballistic table hold over for	18	inches
389 yards level fire
Horizontal leg of the triangle	321	Yards
Ballistic table hold over for	8.5	inches
321 yards
Error if horizontal leg is used	−9.5	inches
Ballistic table hold over for	39.5	inches
500 yards level fire (no
compensation for incline)
Error if no compensation for	+21.5	inches
incline

Rangefinder with Ballistic Range Calculation

The above-described methods may be implemented in a portable handheld laser rangefinder 50, an embodiment of which is shown in FIG. 6, including a laser ranging system 54 having a lens 56 through which a laser beam is emitted and reflected laser light received for determining a range to the target. Rangefinder 50 may be targeted using an integrated optical targeting sight 60 including an objective 62 and an eyepiece 64, through which a user views the distant target. A power button 66 turns on certain electronics of rangefinder 50, described below with reference to FIG. 9, and causes rangefinder 50 to emit laser pulses and acquire range readings. A pair of menu interface buttons 68 are provided on rangefinder 50 for operating menus for inputting setup information and enabling functions of the rangefinder, as described in more detail in U.S. patent application Ser. No. 11/265,546, filed Nov. 1, 2005, which is incorporated herein by reference.

FIG. 7 shows elements of a display 70 which is preferably placed in the field of view of the targeting sight 60 of rangefinder 50. Display 70 is preferably formed by a transmissive LCD display panel placed between objective 62 and eyepiece 64. However, other display devices may be used, including displays generated outside of the optical path of the targeting sight 60 and injected into the optical path of the targeting sight 60, for example by projecting a reticle display onto a prism or beam-combining element (reverse beam splitter). Display 70 may include a circular menu 74 along its perimeter, which can be navigated using buttons 66, 68 to select one or more of various functions of rangefinder 50. The icons labeled >150, 1 st TGT, LAST TGT, M/FT/YD, LOS relate to ranging functions and modes of display. The TBR icon stands for TRUE BALLISTIC RANGE™ and, when selected, activates calculation methods for determining equivalent horizontal range EHR. The icon for BOW toggles between bullet and arrow calculation methods of FIGS. 4 and 5, and between ballistic groupings for bullets and arrows, which are selectable from the menu segments of the A/B/C menu icon.

Display 70 may also include a data display 80 including a primary data display section 82 and a secondary data display section 84. Primary data display section 82 may be used to output EHR calculations, as indicated by the adjacent icon labeled “TBR”. Secondary numerical display 84 may be used to output the LOS range, as indicated by the adjacent icon labeled “LOS”. As shown in FIG. 8, a third data display section 86 is provided for displaying an inclination angle, measured by an inclinometer sensor 110 (FIG. 9) of rangefinder 50. Still further display sections may be provided for displaying data representative of a trajectory parameter, such as ballistic path height BP, vertical ballistic drop, energy, momentum, velocity, etc. at the target range. In one embodiment, based on ballistic path height BP or another trajectory parameter TP, another display section (not shown) may display a recommended holdover adjustment in inches, millimeters, or mils, at the target range or a recommended elevation adjustment in MOA or mils.

As also depicted in FIG. 8, two or more items of data, such as EHR, LOS range, and angle of inclination may be displayed concurrently in display 70. Additional items of data, such as MOA or holdover/drop in inches or mm may also be displayed concurrently in display 70. A battery power indicator 88 is provided in display 70 for indicating an estimate of the amount of battery power remaining. As the batteries in the rangefinder 50 are drained, one or more display segments 89 in the center of the battery power indicator 88 are turned off to indicate the battery power level has dropped. A user-configurable targeting reticle display 90 is also preferably included in display 70, for facilitating aiming of rangefinder 50. The many segments of reticle display 90 allow it to be reconfigured in various ways, such as the one shown in FIG. 8.

FIG. 9 is a block diagram illustrating components of rangefinder 50. With reference to FIG. 9, rangefinder 50 includes a computer processor or digital processor 100, such as a microprocessor or digital signal processor (DSP), operatively coupled to laser ranging system 54, display device 70′, and user interface 66,68. Targeting sight 60 and laser ranging system 54 are aligned relative to each other and supported in a common housing 104, which may include an internal carriage or frame. An inclinometer sensor 110 is mounted to a support structure in rangefinder 50 in alignment with ranging system 54 and targeting sight 60 for measuring the inclination θ of the line of sight (LOS) between vantage point VP and the target T (FIG. 2). The ballistic calculations described above with reference to FIGS. 1-5 may be performed by the digital processor 100 of rangefinder 50 automatically after a laser ranging measurement is made via the ranging system 54.

To facilitate accurate ballistics calculations, digital processor 100 is in communication with inclinometer 110 and other sensors, such as an electronic compass 112, temperature sensor 114, barometer/altimeter sensor 116, and relative humidity sensor 118. The data from these sensors may be used as shooting condition inputs to ballistic calculation software operating on digital processor 100 for performing the methods described above with reference to FIGS. 1-5. A memory 124 readable by digital processor 100 is preferably provided for storing the software program, sensor data, and user-defined settings, among other information. In some embodiments, memory 124 may also store data tables including ballistic coefficients for various bullets and arrows or groups thereof. And in some embodiments, memory 124 may store data tables including ballistic tables with predicted trajectory parameters for known shooting conditions (including a range of angles) and tables with EHR data (under level-fire conditions) for a range of trajectory parameters. A GPS receiver 130 and antenna 132 for acquiring geographic location data from GPS satellite signals may also be included in rangefinder 50 in operative association with digital processor 100. Finally a signaling module 140, which may include an antenna 144, may be coupled to digital processor for transmitting signals representative of ballistic calculation data calculated by digital processor 100, such as one or more trajectory parameters, equivalent horizontal range, elevation adjustments and holdover adjustments.

Graphical Display of Ballistic Holdover Aiming Data

As mentioned above, the output of BP or EHR (step 18, 21, or 26 in FIG. 3) may be displayed via a graphical representation of a corresponding aiming mark of a weapon aiming device reticle or targeting sight. In one embodiment of such a display method, a facsimile of a riflescope reticle is displayed in the display device 70′ of rangefinder 50, then an aiming mark of the facsimile reticle corresponding to the output BP or EHR is identified by highlighting, emphasizing, flashing, coloring, or otherwise changing the appearance of the aiming mark to accomplish a graphical display of the recommended aiming point in relation to the overall reticle pattern. This graphical display communicates to the user which of several aiming marks or points on the corresponding riflescope reticle is recommended for use in holdover aiming of a firearm that is separate from the rangefinder. In another embodiment, the rangefinder 50 and targeting sight 60 are integrated in a common housing with a riflescope or other weapon aiming device, in which case the same sighting device and reticle display may be used for aiming the rangefinder 50 and for aiming the projectile weapon utilizing the graphical holdover aiming display methods described herein. In still another embodiment, BP or EHR data is transmitted via wires or wirelessly by signaling module 140 and antenna 144 of rangefinder 50 for receipt by a riflescope or other aiming device, and subsequent display using the graphical display methods described herein.

FIG. 10 shows a pictorial view of an electronic display 70″ of rangefinder 50, in accordance with one embodiment, including a segmented LCD targeting display 150 which is a facsimile of a ballistic reticle 350 of a riflescope 200 illustrated in FIGS. 12-13. Details of ballistic reticle 350 are described in the '856 application in connection with the Ballistic Aiming System™ (BAS™) technology of Leupold & Stevens, Inc. With reference to FIGS. 9-10, a rangefinder aiming mark 154 of targeting display 150 serves as an aim point of targeting sight 60 for aiming the rangefinder 50 and acquiring a range measurement. Rangefinder aiming mark 154 also represents a primary aiming mark 354 (a/k/a crosshair or center point) of ballistic reticle 350 (FIG. 13) corresponding to a point-blank range or sighted-in range of a weapon 204 (FIG. 12) to which a riflescope 200 or other aiming device incorporating the ballistic reticle 350 is mounted. Targeting display 150 preferably includes heavy posts 156 radiating from the rangefinder aiming mark 154 for guiding the user's eye to aiming mark 154 and for rough aiming in poor light conditions when the finer aiming mark 154 may be difficult to see. Arranged below the rangefinder aiming mark 154 of targeting display 150 are a series of holdover aiming marks including segments 156 of a vertical sight line 160 of targeting display 150 and multiple spaced-apart secondary aiming marks 170, 172, 174, 176. Secondary aiming marks 170, 172, 174, and 176 are shaped similar to and correspond to respective secondary aiming marks 370, 372, 374, and 376 of ballistic reticle 350. As described in the '856 application, secondary aiming marks 370, 372, 374, and 376 are spaced apart below primary aiming mark 354 for accurate indication of bullet drop at corresponding incremental ranges of 300, 400, 450 and 500 yards when the riflescope 200 is sighted in at 200 yards. (As used herein, the term “sighted-in” refers to the calibration or zeroing of the elevation adjustment whereby the point of aim of the primary aiming mark 354 coincides with the point of impact of the projectile on a target at 200 yards.) For improved accuracy, the segments 156 represent ranges in between the incremental ranges of the primary and secondary aiming marks 354, 370, 372, 374, and 376. Of course, the ranges at which the various aiming marks of ballistic reticle 350 may be used to accurately aim the weapon will depend on the sighted-in range, the particular ballistic characteristics of the projectile, and the spacing of the aiming marks, among other factors.

Use of the targeting display 150 and the graphical display method is illustrated in FIG. 11. With reference to FIGS. 9 and 11, a user first aims the targeting sight 60 of rangefinder 50 so that the aiming mark 154 of targeting display 150 is superposed in the field of view over a target 180. While aiming the rangefinder 50 at target 180, the user activates rangefinder 50 by depressing power button 66 (FIG. 6) to trigger a laser ranging measurement of LOS range and subsequent calculation or lookup of ballistic path BP or equivalent horizontal range EHR based on LOS range, inclination angle to target, and other factors, as described above with reference to FIG. 3. The output of BP or EHR is then presented to the user in the form of a graphical identification of the corresponding aiming mark 154, 156, 170, 172, 174, or 176. A numerical display of EHR 182 may also be displayed in electronic display 70″, as depicted in FIG. 11. In the example illustrated in FIG. 11, the EHR to target 190 is determined to be 403.5 yards and the corresponding holdover aiming mark is secondary aiming mark 172 (representing secondary aiming mark 372 of ballistic reticle 350—i.e., the aim point for a target at 400 yards in level-shooting conditions). Secondary aiming mark 172 may be flashed multiple times per second (as illustrated in FIG. 11) or otherwise changed in appearance to identify it and the corresponding secondary aiming mark 372 of reticle 350 as the aiming mark recommended for shooting at the target 180. Other modes of graphical identification include changing a color, size, or brightness of the corresponding holdover aiming mark of targeting display 150.

The above-described method of presenting EHR or BP output in a graphical display that is a facsimile of reticle 350 of the weapon aiming device may help avoid human errors that could otherwise result from attempting to manually convert numerical BP or EHR data or using it to manually determine which of several secondary aiming marks of riflescope reticle 350 should be used to aim the weapon.

To facilitate accurate representation of the holdover aiming point in targeting display 150, the reticle pattern of the display 150 may comprise a collection of independently-controllable display segments, as illustrated in FIGS. 10-11 having a relatively high resolution. In another embodiment (not shown), the entire display 150 may be pixilated and addressable by a display controller so that a single pixel or group of pixels may be selectively flashed or otherwise controlled independently of the others to emphasize a holdover aiming mark corresponding to the BP or EHR. Pixels of a pixilated display could also be driven to generate a display of a selected reticle of a weapon sight (from a menu of reticle styles), a rangefinder setup menu, a rangefinder targeting reticle, a data display, and various other display elements.

Remote Control for Aiming Adjustment

In another embodiment, the BP, EHR, or corresponding aiming mark may be determined by rangefinder 50, but displayed or identified in a separate, remote device, such as a riflescope that receives from the rangefinder device a radio frequency signal representative of the BP, EHR, or corresponding reticle aiming mark. The holdover aiming mark or point may be emphasized or identified in the riflescope reticle by intermittently blinking or flashing the corresponding reticle aiming mark, or by merely displaying the reticle aiming mark while blanking other surrounding reticle features. In other embodiments, the reticle aiming mark may be emphasized relative to other reticle features, by a color change, intensity change, illumination, size or shape change, or other distinguishing effect. In other embodiments, the BP or EHR or other data calculated by rangefinder 50 may be utilized for automated elevation adjustment in a riflescope or other sighting device.

With reference to FIGS. 9 and 12, signaling module 140 and antenna 144 of rangefinder 50 may be configured to send radio frequency signals to riflescope 200 (FIG. 12) mounted on a firearm 204 or to another weapon aiming device (not shown). Radio signals may be used to wirelessly feed or control a reticle display 210 (FIG. 13) of riflescope 200 viewable through a riflescope eyepiece 214 for displaying ballistics data in the field of view and/or for other purposes. Wireless data transmission enables the rangefinder 50 to be separate from the firearm and protected from the effects of recoil and other harsh environmental conditions to which riflescopes are typically exposed. For example, rangefinder 50 may be held by a first person—a spotter—standing several meters away from a shooter holding a rifle 204 with a riflescope 200 that receives data wirelessly from rangefinder 50. Rangefinder 50 may also transmit data wirelessly to several different riflescopes or other devices substantially simultaneously, allowing a single spotter to provide data to a group of shooters.

In one embodiment, the signals transmitted by signaling module 140 may include information representative of elevation adjustments to be made in riflescope 200 (in minutes of angle (MOA) or fractional minutes of angle, such as ¼ MOA or ½ MOA) based on ballistics calculations made by digital processor 100. Elevation adjustments expressed in MOA or fractions thereof may be displayed in reticle 210 or effected in riflescope 200 via manual adjustment of an elevation adjustment knob 220, a motorized elevation adjustment mechanism, or other means, such as by controlling or shifting reticle display 210 or reticle 350 for offsetting an aiming mark in the amount of aiming adjustment needed, or to show, highlight, or emphasize a fixed or ephemeral aiming mark corresponding to the EHR calculated by digital processor 100. The kind of data needed to make such an adjustment or aiming mark may depend on whether riflescope reticle 210 is in the front focal plane or the rear focal plane of riflescope 200.

When the recommended elevation adjustment is displayed (in MOA or otherwise) in the reticle display 210 of riflescope 200, it may be updated dynamically as the user manually adjusts an elevation setting of riflescope 200 via an elevation adjustment knob 220 or other means. To enable the recommended elevation adjustment display to be updated dynamically, the elevation adjustment knob 220 may include a rotary encoder that provides feedback to a display controller of the riflescope 200 or to the digital processor 100. Dynamic updating of the recommended elevation adjustment may enable the reticle display 210 to show the amount of adjustment remaining (e.g., remaining MOA or clicks of the adjustment knob needed) as the user adjusts elevation, without requiring constant communication between the riflescope 200 and rangefinder 50 during the elevation adjustment process. Dynamic updating of the remaining adjustment needed may facilitate operation of the rangefinder 50 and the riflescope 200 sequentially by a single person. In another embodiment, the rangefinder 50 may communicate constantly with riflescope 200, which may allow two people (e.g., a shooter working with a spotter) to more quickly effect accurate aiming adjustments.

Signaling module 140 may include an infrared transceiver, Bluetooth™ transceiver, or other short-range low-power transceiver for communication with a corresponding transceiver of riflescope 200, for enabling 2-way communication while conserving battery power in rangefinder 50 and riflescope 200. Data for controlling reticle 210 and elevation adjustment mechanism 220 may be transmitted via Bluetooth or other radio-frequency signals. Also, because Bluetooth transceivers facilitate two-way communication, the rangefinder 50 may query riflescope 200 for a current elevation adjustment setting, a power adjustment setting, and other information, such as the type of riflescope 200 and reticle 210 used. This data may then be taken into account in ballistics calculations performed by digital processor 100. Elevation adjustment and power adjustment settings of riflescope 200 may be determined by rotary position sensor/encoders associated with elevation adjustment knob 220 and power adjustment ring 230, for example.

Alternatively, signaling module 140 may include a cable connector plug or socket for establishing a wired connection to riflescope 200. A wired connection may avoid the need to have delicate electronics and battery power onboard riflescope 200. Wired and wireless connections may also be made between signaling module 140 and other devices, such as bow-sights (including illuminated pin sights and others), PDAs, laptop computers, remote sensors, data loggers, wireless data and telephone networks, and others, for data collection and other purposes.

Holdover indication in a riflescope, bow sight, or other optical aiming device may be achieved by emphasizing an aiming mark of the sight that corresponds to the EHR calculated by rangefinder 50. In ballistic reticle 350, a primary aiming mark 354, which may be formed by the intersection or convergence of a primary vertical aiming line 360 with a primary horizontal aiming line 362, coincides with a reference sighted-in range (such as 200 yards horizontal). As described above and in the '856 application, secondary aiming marks 370, 372, 374, and 376 are spaced along primary vertical aiming line 360 and identify holdover aiming points at which bullet impact will occur at incremental ranges beyond the sighted-in range.

As illustrated in FIG. 13, secondary aiming marks 370, 372, 374 and 376 of reticle 350 are designated by three spaced-apart aiming marks, including converging arrow heads and hash marks crossing the primary vertical aiming line 260. The various aiming marks and lines of reticle 350 may be independently controllable for display or emphasis, such as by flashing one or more of the aiming marks in the field of view of the rangefinder, in a manner similar to the way in which elements of rangefinder targeting display 150 of FIG. 10 are identified, as described above. In response to signals received from rangefinder 50, a selected one of the primary or secondary aiming marks 354, 370, 372, 374, 376 corresponding most closely to the EHR may be displayed, intermittently flashed, or otherwise emphasized to graphically indicate to the shooter which of the aiming marks should be used to aim firearm 204. This greatly simplifies aiming adjustment.

Unlike an automatic adjustment of the elevation adjustment (e.g., via a motorized knob 220), a graphical display of the holdover aiming adjustment in reticle 350 of riflescope 200, may give a user increased confidence that the aiming adjustment has been effected properly and that no mechanical malfunction has occurred in the elevation adjustment. Graphical display of aiming adjustment in the reticle display also allows the shooter to retain complete control over the aim of riflescope 200 and firearm 204 at all times, may reduce battery consumption, and may eliminate possible noise of adjustment motors of knob 220.

It will be obvious to those having skill in the art that many changes may be made to the details of the above-described embodiments without departing from the underlying principles of the invention. The scope of the present invention should, therefore, be determined only by the following claims.

Claims

1. A method for aiming a projectile weapon that shoots a selected projectile having associated ballistic characteristics, comprising: obtaining a list of multiple types of projectiles and associated predetermined projectile groups, wherein each predetermined projectile group encompasses multiple types of projectiles on the list having similar ballistic characteristics, wherein each projectile group corresponds to one of multiple ballistic compensation settings;from the list, identifying the ballistic compensation setting corresponding to the projectile group encompassing the selected projectile;determining a range from a vantage point to a target;measuring an angle of inclination between the vantage point and the target;based on the range to the target, the angle of inclination, and the identified ballistic compensation setting, automatically determining an aiming adjustment for the projectile weapon; andaiming the projectile weapon based on the aiming adjustment.

2. The method of claim 1, wherein the selected projectile is a type of ammunition and each of the predetermined projectile groups encompasses multiple different types of cartridges having different loads and calibers of ammunition.

3. The method of claim 2, wherein each predetermined projectile group includes at least two mutually exclusive types of cartridges.

4. The method of claim 1, wherein the predetermined projectile groups include first and second mutually exclusive groups of ammunition.

5. The method of claim 1, further comprising adjusting a setting of an aiming device based on the identified ballistic compensation setting.

6. The method of claim 1, wherein the aiming adjustment includes a holdover adjustment.

7. The method of claim 6, further comprising displaying the holdover adjustment.

8. The method of claim 1, wherein the step of determining the range to the target includes using a laser rangefinder to measure a line-of-sight distance from the vantage point to the target.

9. The method of claim 8, wherein the step of automatically determining an aiming adjustment includes predicting a trajectory parameter expected for the selected projectile if the selected projectile were to be shot at the target without any aiming adjustment, wherein the trajectory parameter is predicted for the point on a trajectory path closest to the target location.

10. The method of claim 9, wherein the step of automatically determining an aiming adjustment includes: based on the trajectory parameter, determining an equivalent horizontal range at which the trajectory parameter would occur if shooting the projectile from the vantage point toward a theoretical target located in a horizontal plane intersecting the vantage point.

11. The method of claim 1, wherein the predetermined projectile groups include at least a predetermined first group and a predetermined second group, the first and second groups having different nominal ballistic characteristics, the ballistic characteristics of the types of projectiles associated with the first group falling within a first acceptable error tolerance from the nominal ballistic characteristic of the first group, and the ballistic characteristics of the types of projectiles associated with the second group falling within a second acceptable error tolerance from the nominal ballistic characteristic of the second group.