1. Field of the Invention
The present invention relates generally to rifled barrels for firearms. Particularly the present invention relates to firearm barrels which may fire subsonic ammunition with high flight trajectory precision.
2. Description of the Related Art
The term accuracy is often used when referring to firearms. A less used but far more important term is precision. As defined herein, precision is the repeatability of a given process. As defined herein, accuracy is the closeness of the result of the process to the desired result. In reference to firearms, the repeatability of the impact point of a bullet upon a target at a given distance is of utmost importance. The impact point repeatability is most affected by the precision of the flight trajectory of the bullet. A precise flight trajectory requires the bullet fly in a consistent and repeatable arc thru the atmosphere with little deviation from shot to shot. With a precise i.e. repeatable flight trajectory, the sights of the firearm may be adjusted to achieve the desired accuracy of the impact point upon the target. Stated another way, a firearm may fire a bullet with a given flight trajectory precision and then the firearm sights adjusted to achieve the best accuracy upon the target which that flight trajectory precision allows.
In many firearm and cartridge combinations, the bullet exits the barrel at a super-sonic velocity, in some excess of the speed of sound. In flight, drag upon the bullet may slow the round to a sub-sonic velocity prior to impacting the intended target. In many situations within the firearm community, a sub-sonic bullet is preferred. In these cartridges and firearm combinations, the cartridge powder charge and barrel combination results in the bullet leaving the muzzle of the barrel at a sub-sonic velocity. In the atmosphere on a standard day at sea level static conditions, the speed of sound is approximately 1,100-1,125 feet per second. As will be appreciated by those skilled in the art, the speed of sound varies with height, temperature, humidity, and other secondary factors. A cartridge powder charge may be designed for any given firearm such that the bullet exits the barrel at a velocity below 1,100 feet per second. As defined herein, the term firearm includes both rifles and pistols with any barrel length and cartridge combination.
Achieving flight trajectory precision with a sub-sonic bullet has proven difficult with many firearms. The lack or precision of the flight trajectory results in an unacceptable scatter of the flight paths of the bullets and ultimately a scatter in the impact point upon the target from shot to shot. Stated another way, there is poor repeatability in the sub-sonic bullet flight trajectory or path from a given firearm from shot to shot. Of paramount importance to the precision of the sub-sonic bullet flight trajectory is the firearm barrel design. The slow forward velocity of the bullet means that any mass imbalance or streamlining imbalance of the body of the bullet effectively has a longer period of time to disturb the bullet flight trajectory at any given range. The relatively slow rotation of the sub-sonic bullet also reduces the gyroscopic effect of the spinning bullet, making any asymmetric weight distribution within the fired and obturated bullet more apparent. The symmetry in the obturated bullet body and lands swaged upon the bullet body are of critical importance to the precision of the bullet flight trajectory.
According, it would be advantageous to provide a barrel design to optimize the flight trajectory precision of a sub-sonic round from a firearm. The barrel design would uniformly obturate the sub-sonic fired bullet. The base of the fired bullet and the lands formed thereon would be uniform to allow for precision flight characteristics of each sub-sonic bullet fired. The groove design of the barrel would provide lands which optimize the trans-sonic and sub-sonic bullet flight trajectory precision within the barrel and exiting the barrel. In flight, the lands formed upon the bullet by the barrel design would optimize the precision of the bullet flight trajectory in both the sub-sonic and transonic flight regimes. It is thus to such a sub-sonic high precision firearm barrel that the present invention is primarily directed.
The disadvantages of the prior art are overcome by the present invention which, in one aspect, is a barrel for use in a firearm. The barrel has a central axis and a central bore formed around the central axis. The central bore has a bore diameter. The barrel has a chamber for receiving a cartridge therein, the chamber configured to receive a cylindrical cartridge case with a bullet engaged within the cartridge case. The bullet has a nominal bullet diameter, and the cartridge case containing a propellant, the propellant producing a propellant pressure upon ignition of the propellant. The barrel has a plurality of rifling grooves within the bore, the outer diameter of the grooves defining a groove diameter, the groove diameter being within .0003 inch of the nominal bullet diameter and the barrel has at least 10 rifled grooves. Each of the plurality of rifling grooves has a sidewall formed from the bore diameter to the groove diameter, wherein the sidewalls formed are substantially parallel and the depth of each of the rifling grooves is shallow. Wherein the rifled grooves have a twist angle to spin the bullet as it is forced down the bore, the twist angle formed between the groove and the central axis of the bore. The groove twist angle imparting a twist rate upon the bullet. Upon ignition of the propellant, the bullet is forced by propellant pressure out of the cartridge case and into the rifled bore of the barrel. The propellant pressure then forcing the bullet out the end of the barrel at a subsonic velocity.
The bullet being obturated as it is forced down the bore, the plurality of shallow barrel grooves forming a plurality of raised lands upon the bullet. The obturated bullet having at least 50% lands formed around the circumference of the bullet body. Wherein the buffeting effect upon the bullet in flight by a normal shock wave upon the raised bullet lands is reduced by the plurality of bullet lands and the reduced height of each of the plurality of bullet lands.
In another aspect of the present invention, the driven edge of the bullet land is 90 to 95 degrees to the reference edge and the trailing edge of the bullet land is between 0 and 20 degrees to the reference edge. The buffeting effect upon the bullet in flight by turbulence across the trailing edge bullet land is reduced.
In yet another aspect of the present invention, the buffeting effect of the propellant pressure upon the bullet from an imperfection in any one rifling groove is reduced by at least 50% and the buffeting of the bullet as the bullet exits the barrel and transitions to flight is reduced. In yet another aspect of the present invention, as the bullet is forced down the barrel bore, the sealing of the propellant pressure behind the bullet and between the bullet and barrel bore is improved by the plurality of shallow rifling grooves.
These and other aspects of the invention will become apparent from the following description of the preferred embodiments taken in conjunction with the following drawings. As would be obvious to one skilled in the art, many variations and modifications of the invention may be affected without departing from the spirit and scope of the novel concepts of the disclosure.
The present invention provides a barrel for use in a firearm that improves the accuracy of both sub-sonic and super-sonic projectiles fired from the barrel. The barrel improves the sealing and possible mass imbalance of the obturated bullet due to smearing, erosion, or inconsistencies in each of the bullet lands and in the obturated bullet body. The barrel stabilizes the transitional flight dynamics as the bullet leaves the end of the barrel at the muzzle. The trans-sonic and subsonic flight characteristics of the bullet are also improved by a more aerodynamic surface along the body of the bullet and by an angled sidewall on the trailing edge bullet land.
A firearm barrel is configured for a particular cartridge which may be a rifle or a pistol cartridge. The barrel bore is sized to accept and engage the bullet of the cartridge and the barrel chamber is configured to accept the cartridge body shape. The firearm barrel has a central bore running from the barrel chamber, thru the body of the barrel, and exiting the barrel at the muzzle. The barrel chamber is as concentric and colinear with the barrel bore as manufacturing tolerances allow. The barrel bore has multiple equally spaced rifles, also called rifling grooves, cut into the bore sidewall. The barrel bore then has a diameter down the length of the bore and the barrel has a rifled diameter measured at the bottom of each rifling groove. The rifles spiral around the bore at a constant rate or twist. The rifling diameter is typically .0002 below the nominal diameter of the bullet within the cartridge. Typically, the depth of each barrel rifling is .003 to .005 inch into the barrel bore which results in a rifling diameter of approximately .006 to .010 inch larger than the barrel bore. In a common prior art configuration, the barrel rifling is .004 inch into the barrel bore, and the rifling diameter is .008 inch.
When the propellant, or gunpowder, within the cartridge is ignited, the cartridge bullet is forced from the cartridge and into the bore of the barrel by the propellant pressure. The bullet body is initially larger than the barrel bore minor diameter. The bullet is obturated by the barrel bore wherein the diameter of the bullet body is reduced to the barrel bore diameter, the bullet increases in length slightly, and lands are formed or swaged upon the bullet body corresponding to the rifling grooves in the barrel. The lands swaged upon the bullet engage in the rifling groves and the bullet is spun within the bore. Distortion of the lands on the bullet body, wherein the bullet does not rotate in sequence with the spiraling rifling of the bore during obturation, is called smearing. As defined herein, the bullet body is that portion of the bullet outer surface that engages the barrel bore and rifling grooves.
The obturation of the bullet is a quick, violent, and often imperfect process. The bullet lands may be imperfectly formed as the bullet begins to spin in the bore, the base of the bullet may be distorted or non-symmetrical about the barrel bore axis, and the mass distribution of the obturated bullet about the central axis of the bullet may be mass unbalanced. Stated another way, the lands of the bullet may smear of not fully form, the bullet base may not obturate evenly, and the bullet may have more or less material and mass at some points around the obturated bullet body than at others.
As depicted in
There are generally two types of bullet designs, flat base bullets and boat tail bullets. The ballistic coefficient “BC” of a bullet is a measure of the bullets ability to overcome air resistance in flight. Stated another way, it's the ratio of the bullet's sectional density to its coefficient of form. In short, a high ballistic coefficient is indicative of a rounds ability to resist drag. When a bullet has an initial sub-sonic velocity when leaving the barrel, the ability of the bullet to resist drag and therefore resist slowing in velocity, becomes more critical. Boat tail bullets generally have a higher ballistic coefficient when flying thru the air than blunt base or flat base bullets. Stated another way, boat tail bullets are more streamlined in flight and less affected by air resistance. Flat base bullets may do a better job at sealing the hot propellant gases within the barrel bore behind the obturated bullet, however flight trajectory precision is generally poor. When boat tail bullets are employed, the hot propellant gases are more likely to interfere with the bullet obturation process and cause the bullet to be overtaken and surrounded by the hot propellant gases within the bore. The hot propellant gases cause side erosion on the bullet body and lands. This erosion may cause a mass imbalance on the obturated bullet, destabilize the flight of the bullet thru the air, and adversely affect the precision of the flight trajectory of the bullet.
As further depicted in
As depicted in
In the 12 groove illustrative embodiment of
As depicted in
In flight, any dynamic imbalance to the spinning mass of the bullet is minimized because the uniformly obturated bullet mass is more uniform about the axis of spin of the bullet. The 12 rifle groove barrel of this exemplary embodiment of the present invention provides at least a 50% less felt effect from inconsistencies in the land to land dimension and mass of the bullet in flight. Stated another way, any inconsistencies in the height or width of a single land of the bullet of the present invention has a 1/12 proportional effect upon the bullet flight precision as compared to the 1/4 proportional effect of an inconsistency in a land in a bullet fired from a 4 groove barrel of the prior art. In the present invention, the multiple shallow lands (12 lands) of the bullet are well formed and the bullet experiences less dynamic imbalance, and experiences less turbulence and buffeting from the lands engaging the incoming air stream. As defined herein, turbulence is violent or unsteady movement of air about the bullet body. As defined herein, buffeting is an irregular oscillation of the bullet caused by turbulence.
As depicted in
Another embodiment of the present invention is depicted in
Another important regime of bullet flight path precision ballistics is the flight of the bullet thru the air of the atmosphere.
In another alternative embodiment of the present invention,
In the bullet 120 fired from the prior art barrel of
As will be appreciated by those skilled in the art, we reach a tipping point, or flip in flight dynamics of the bullet as the land surface exceeds the groove surface of the bullet. In bullet flight, the surface presented to the incoming atmosphere from a bullet body with high lands of the prior art, to a primarily bullet outer surface of lands but with only shallow groves in the present invention. In regard to the bullet in flight, due to the greater surface area of the riffling peaks vs valleys of the present invention in contrast to a prior art 4-6 groove riffled bullet, the air in the valleys creates a shielded pocket, thus creating high pressure bridge or cushion of air that lies in the grooves that has an independent air flow from the air traveling around the outer bullet land peaks. In flight, the incoming atmosphere or air blast traveling along the outside surface of the bullet, fired from the barrel of the present invention, rides along the land peaks and spans across the grooves. The air blast rides across the outer diameter of the bullet without infiltrating the grooves and creating turbulence and associated buffeting of the bullet flight trajectory. A bullet fired from the barrel of the present invention presents greater than 66% of the bullet body circumference, and subsequently outer surface of the bullet body, as consistent raised lands to the incoming air blast. The remaining bullet body circumference being made up by the shallow grooves. As will be appreciated by those skilled in the art, in the barrel of the present invention the fired bullet circumference land to groove ratio may be between 50% to 90% land circumference for differing riffling counts and barrel designs of the present invention.
A cross section of a bullet 120 fired from the 4 groove barrel of the prior art is depicted in
In the barrel configurations of the prior art, the LDE angle and the LTE angle swaged upon the bullet are the same and between 0 degrees to 5 degrees to the reference edges of the bullet. Correspondingly, a bullet fired from the barrel of the prior art has a bullet land which is obturated or swaged upon it which is narrow at the outer surface of the land and is parallel or tapers to a wider base at the bullet body.
As will be appreciated to those skilled in the art, as a subsonic bullet is traveling thru the air, the bullet is initially spinning at a rate corresponding to the twist rate of the barrel at the bullet velocity. The bullet spin direction is depicted by Arrow “T”. As the bullet travels downrange, the forward velocity of the bullet slows at a rate faster than the spin rate of the bullet slows. Stated another way, the air impacting the front of the fired bullet slows the bullet forward velocity far faster than the spin rate of the bullet slows. As the sub-sonic bullet travels downrange, the bullet is spinning faster then the forward velocity of the bullet justifies and the lands of the bullet effectively auger or screw thru the incoming air blast. The angle of the land trailing edge sidewall of the bullet becomes more critical to the bullet flight path precision as the incoming air blast is encountering the land trailing edge and not the land driven edge in the overspinning bullet.
As further depicted in
Another alternative embodiment of the present invention is presented in
As depicted by Arrows “P” in
The exemplary embodiments of the invention herein all depict a 12 groove barrel. As will appreciated by those skilled in the art, any barrel with 8 or more grooves may benefit from the present invention.
While there has been shown a preferred embodiment of the present invention, it is to be understood that certain changes may be made in the forms and arrangement of the elements of the sub-sonic high precision firearm barrel without departing from the underlying spirit, scope, and essential characteristics of the invention. The present embodiment is therefore, to be considered as merely illustrative and not restrictive, the scope of the invention being indicated by the claims rather than the foregoing description, and all changes which come within the meaning and range of equivalence of the claims are therefore intended to be embraced therein.
Number | Name | Date | Kind |
---|---|---|---|
2293114 | Carter | Aug 1942 | A |
2967369 | Walton | Jan 1961 | A |
3100358 | Robinson | Aug 1963 | A |
4660312 | A'Costa | Apr 1987 | A |
6070532 | Halverson | Jun 2000 | A |
11280599 | Billings | Mar 2022 | B2 |