Patent Grant
8333029
The invention relates to firearms, and more particularly to a gun barrel that is manufactured to withstand temperatures exceeding 800° F. during the course of an extended firing schedule.
Gun barrels are traditionally manufactured from various steel alloys. Lining the gun barrels with various other materials to provide enhanced corrosion resistance, increased projectile velocity, and lengthened service life has been a routine practice for small arms for over 100 years.
Increased use of hotter burning gunpowder to increase projectile performance and fully automatic firing to increase rounds per minute cause gun barrels to reach temperatures exceeding 800° F. Maintaining gun barrel integrity and minimizing erosion to prolong gun barrel life has become very challenging under these conditions.
416 Society of Automotive Engineers (SAE) grade stainless steel has been used for gun barrels to prevent corrosion, but is generally not as well suited for use as a gun barrel compared to 4140 SAE grade and 4150 SAE grade chromoly steels. Chromoly steels provide better strength at the high temperatures reached during extended periods of fully automatic firing, which makes them very popular for use in military small arms such as the M-16 rifle.
Unfortunately, chromoly steels are vulnerable to corrosion and rapid erosion. Barrel bore rusting caused weapon malfunctions during the Vietnam War because the 4150 SAE grade chromoly steel barrels rusted in the humid environment. It was also learned that the high-pressure projectile fired by the M-16 rapidly eroded the chamber of the barrel. A chrome lining was applied to the barrel in order to extend the weapon's surface life.
Chrome-lined barrels present several of their own problems, though. First, it is very difficult to apply the chrome evenly in large production runs. Inconsistent application adversely affects the rifle's accuracy. Chrome lining also prevents the barrel from operating at temperatures exceeding 800° F. for any prolonged period of time, which limits the number of rounds that can be fired before the gun barrel must be permitted to cool. Otherwise, the barrel will lose its temper quickly, resulting in erosion of the barrel chamber and firearm malfunctions.
Other linings, such as the one described in U.S. Pat. No. 7,197,986, have been proposed, but they do nothing to increase the strength of the barrel at higher temperatures. The coating described is limited to protecting the chamber and rifling of the barrel. However, when a firearm is operated for long periods of time at high temperatures, preserving the temper of the barrel itself is the primary problem that must be overcome.
Alternative barrel materials, such as the composite gun barrel described in U.S. Pat. No. 6,889,464, provide a lightweight alternative to steel that cools faster than a standard gun barrel. Unfortunately, the resins used in the gun barrel's construction are not suitable for sustained high rates of fire. Eventually, the high heat generated causes the resin to break down, rendering the gun barrel unusable.
It is therefore an object of this invention to provide a gun barrel that maintains its temper and has increased corrosion resistance for extended operation of fully automatic firearms.
The present invention provides an improved gun barrel, and overcomes the above-mentioned disadvantages and drawbacks of the prior art. As such, the general purpose of the present invention, which will be described subsequently in greater detail, is to provide an improved gun barrel that has all the advantages of the prior art mentioned above.
To attain this, the preferred embodiment of the present invention essentially comprises a body having a central bore including a front opening and a rear opening. The rear opening of the body includes a chamber formed to receive a cartridge. The body has a surface layer covering all surfaces of the body. The body has a diffusion layer extending below the surface layer into an underlying material of the body. The central bore may have rifling defined by lands and grooves formed in the bore. An interior portion of the body may have a hardness of at least 50 HRC and not greater than 55 HRC after the surface layer and diffusion layer are created on the body. The surface layer and diffusion layer may be created by subjecting the body to a ferritic nitrocarburizing treatment followed by an oxy nitrocarburizing treatment. The nitrocarburizing treatments may be repeated. The body may be AISI H13 grade tool steel.
There are, of course, additional features of the invention that will be described hereinafter and which will form the subject matter of the claims attached.
There is thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood and in order that the present contribution to the art may be better appreciated.
A preferred embodiment of the gun barrel of the present invention is shown and generally designated by the reference numeral 1.
As used in the specification, the word “front” or “forward” corresponds to the firing direction of the firearm (i.e., to the right as shown in
The diffusion layer 3 extends from the outer black oxide surface layer into the underlying material of the gun barrel. The diffusion layer extends beneath the black oxide surface layer beginning at a depth of 0.001 inch from the surface of the gun barrel for about an additional 0.015 inches. This is in contrast to a surface coating, which does not affect the underlying barrel material. A core 8 of non-nitrided, but still hardened, material is located in the interior of the gun barrel between the diffusion layers.
In the current embodiment, the gun barrel is an M4 carbine gun barrel manufactured from American Iron and Steel Institute (AISI) H13 grade tool steel. Alternative hard refractory materials commonly referred to as tool steels, such as any other AISI H-grade tool steel, any AISI M-grade tool steel, and any AISI T-grade tool steel, can also be used.
After the initial hardening, the bar of steel are cut to the desired length (28 inches to produce two M4 carbine barrels), gun drilled, and bore reamed. During the deep hole gun drilling process, the barrel is spun on its longitudinal axis at about 3500 revolutions per minute while a non-rotating carbide-tipped drill is fed at 1⅛ inches per minute into the center of the barrel. The drill is specially ground to a profile (20° outside/quarter, 30° inside/half) that seeks the gravitational center of the spinning steel bar so the resulting hole is registered with the longitudinal axis of the barrel. Cuttings from the barrel are cleared by a high-pressure flow of oil that passes through the hollow core of the drill. Alternatively, the bar of steel can be stationary and the drill can rotate during the deep hole gun drilling process.
Once the drill has passed completely through the barrel, the barrel is placed in a bore reaming machine and mounted in a stationary position. The bore reamer is placed through the hole previously drilled in the center of the barrel, spun at 500 revolutions per minute, and pulled through the barrel at a linear speed of about 1.5 in. per minute. The cuttings are cleared from the barrel by a pressurized cutting oil supply that passes through the hollow core of the bore reamer. These actions complete the step of machining the barrel (10) and form a bore that is registered with the longitudinal axis of the barrel.
After the barrel has been machined, the bore is hand lapped in step (11) using a lead lap impregnated with aluminum oxide particles to remove any tooling marks left behind by the bore reaming process. The barrel is then cleaned with solvents and dried prior to being mounted in a button rifling machine. Step (11) is completed by button rifling the bore to create lands and grooves, performing another hand lapping, and turning the gun barrel on a lathe to finish the gun barrel's external dimensions.
During button rifling, an oversized button is pulled through the barrel by the hydraulic piston of the button rifling machine. The button is an oval-shaped piece of hardened carbide with a desired amount of equally spaced relief cuts around its major diameter. These cuts are voids to allow the bore diameter turning the same wildly oval major diameter pushes the steel into a new groove diameter. The button is rotated by guide on the button rifling machine to provide the desired twist per foot. Once the button has passed completely through the barrel, the lands are left behind at the previous bore diameter, resulting in the barrel having a rifled center. Alternatively, hammer-forged or cut rifling can be used instead of button rifling.
The second hand lapping in step (11) also uses a lead lap impregnated with aluminum oxide particles and orients the land and groove surfaces with the helical twist of the rifling. This step of the process ensures that the projectile will not experience mechanical abrasion as it travels down the bore. The lapping process is also a critical preparatory phase for the surface conversion process that occurs when the black oxide surface layer is created.
In step (12) the barrel is chambered by a five-blade carbide reamer at approximately 400 RPM. The feed rate is approximately ½ inch per minute. This is accomplished by removing material from the rear of the barrel to create a negative of a firearm cartridge. A cartridge is an assembled unit consisting of a casing, primer, propellant, and projectile. The barrel is now ready for hardening and tempering.
Finally, in step (13), the barrel is subjected to a surface conversion process that also tempers the hardened barrel. First, the barrel is preheated in air at a temperature between 650° F.-750° F. for 30 minutes. This initial heating prevents any thermal shock to the barrel as the barrel is lowered into the Austenitize process, which heats the barrel to 1850° F. for 120 minutes. Austenitization means to heat the iron, iron-based metal, or steel to a temperature at which it changes crystal structure from ferrite to austenite. Austenite, also known as gamma phase iron, is a metallic non-magnetic allotrope of iron or a solid solution of iron, with an alloying element.
The barrel is then moved to a nitriding bath for a time of 90 minutes at a set temperature of 1070° F. In the current embodiment, a ferritic nitrocarburizing process using a salt bath of alkali cyanate is employed. However, any suitable nitriding technique that imparts a diffusion layer to the barrel could be used. The cyanate thermally reacts with the surface of the work piece to form alkali carbonate. The bath is then treated to convert the carbonate back to a cyanate. The surface formed from the reaction has a compound (surface) layer and a diffusion layer. The compound layer consists of iron, nitrogen, and oxygen, is abrasion resistant, and stable at elevated temperatures. The diffusion layer contains nitrides and carbides.
After the first nitriding process is complete, the barrel is cooled in an oxidative cooling bath with a set temperature of 825° F. for 10 minutes to undergo oxy nitrocarburizing. The barrel is then returned to the nitride bath for 90 minutes at 1070° F. followed by another 10 minutes in the oxidative cooling bath at 825° F. At the conclusion of the baths, the barrel has undergone two ferritic nitrocarburizing treatments and two oxy nitrocarburizing treatments.
The final cooling bath allows the barrel to cool before the barrel is placed in the water cleaning stage of the process. Also, oxidation takes place on the surface of the components by forming a thin iron oxide layer on the compound layer and sealing the pores that are opened during the nitriding process with oxide. This oxide layer produces the black coloration of the gun barrel.
The barrel is then raised from the oxidation bath and allowed to air cool for an average time of 10-20 minutes before being lowered into a water rinse.
The water rinse stage is used to clean the oxidation bath residue from the barrel and cool the barrel further. This stage is typically a 15-20 minute process.
Cleaning is performed in an additional water rinse for a minimum of 30 minutes.
The barrel is then dipped in a post process oil treatment for even more enhanced corrosion resistance to complete step (14).
The resulting black oxide surface layer has a hardness of at least 68 HRC and not greater than 72 HRC. This range of hardness provides the desired level of resistance to wear without being too brittle. The black oxide surface layer is 2 points harder than a chrome coating, which makes the surface layer more durable than a chrome coating. In addition, the surface the bullet contacts has much more similar properties to the other material comprising the barrel than a chrome coating does to conventional gun barrel steel. The black oxide surface layer has a similar thermal expansion rate to the underlying H13 tool steel, so the surface layer is much less prone to breaking off in chunks as the gun barrel undergoes heating and cooling cycles compared to a hard chrome coating or a nitrided gun barrel made from a softer and more elastic material than H13 tool steel. H13 tool steel maintains integrity between the core material and the surface oxide layer. Other similar alloy tool steels can be used to provide a similar result. H13 tool steel is preferred because it retains hardness and wear resistance in extreme heat, even more so than other tool steels.
Nitriding a conventional gun barrel steel will cause chunks of the surface layer to break off from the underlying material because the surface layer is much harder than the host steel and cannot maintain structural integrity. Conventional gun barrel steel has much different thermal expansion rate than oxide surface layer.
The black oxide surface layer extends the service life of the gun barrel by protecting the surfaces of the chamber, the gun barrel's rifling, and the gas port and enhancing the gun barrel's corrosion resistance. The black oxide surface layer also reduces friction between the barrel chamber and a spent cartridge to reduce erosion of the chamber and facilitate cartridge extraction. The black oxide surface layer also reduces friction between the bore and a discharged projectile to reduce erosion of the bore. The surface layer makes the surfaces of the gun barrel wear resistant, lowers the coefficient of friction, and reduces tendencies for welding or seizing with other metallic parts.
The hardness of the diffusion layer 3 resulting from step (13) is a gradient from 68 to 72 HRC down to 50 to 55 HRC based on proximity to the core 8. The diffusion layer hardens the gun barrel to a deeper level to enable the gun barrel to maintain its temper at high temperatures. In fact, the gun barrel of the current invention can be operated at temperatures up to 1000° F. without losing its temper. This affords the user of the opportunity to use their firearm for firing schedules which would destroy or significantly reduce the useful life of other currently available barrels. Furthermore, even as the blackened oxide surface layer erodes, the lands in the bore are still harder at their core than either non-nitrided H13 or the lands of a hard chrome-lined gun barrel because of the diffusion layer. The diffusion layer is also more corrosion resistant than a hard chrome-lined gun barrel once the lining is worn away and the underlying barrel material is exposed.
As a result of step (13), the core of the wall of the barrel is hardened to a hardness of at least 50 HRC and not greater than 55 HRC. This is accomplished by the heat associated with the nitriding process. This range of hardness makes the gun barrel as hard as possible without becoming brittle. It gives the gun barrel sufficient rigidity and durability with desired elasticity. If the gun barrel were softer, it would be more susceptible to losing temper as it is heated to a high temperature during extreme rates of fire and then subsequently cooled.
Unless otherwise indicated, all steel grades referenced in the specification have the specified formulations designated by the United States Society of Automotive Engineers (SAE).
While a current embodiment of mounting system has been described in detail, it should be apparent that modifications and variations thereto are possible, all of which fall within the true spirit and scope of the invention. With respect to the above description then, it is to be realized that the optimum dimensional relationships for the parts of the invention, to include variations in size, materials, shape, form, function and manner of operation, assembly and use, are deemed readily apparent and obvious to one skilled in the art, and all equivalent relationships to those illustrated in the drawings and described in the specification are intended to be encompassed by the present invention. Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.
The present application claims priority to and is a continuation-in-part of U.S. patent application Ser. No. 12/005,984, now abandoned, entitled “NOVESKE RIFLEWORKS EXTREME DUTY MACHINE GUN BARREL,” filed Dec. 28, 2007, which claims priority to U.S. Provisional Patent Application Ser. No. 60/899,784, entitled “NOVESKE RIFLEWORKS EXTREME DUTY MACHINE GUN BARREL,” filed Feb. 5, 2007.
| Number | Name | Date | Kind |
|---|---|---|---|
| 1316509 | Rose | Sep 1919 | A |
| 2848401 | Hartley | Aug 1958 | A |
| 6564689 | Billgren | May 2003 | B1 |
| Number | Date | Country | |
|---|---|---|---|
| 60899784 | Feb 2007 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12005984 | Dec 2007 | US |
| Child | 13065207 | US |
