Gas check
Encyclopedia
A gas check is a device used in some types of firearms ammunition
. Gas checks are used when non-jacketed bullets
are used in high pressure
cartridges
, to prevent the buildup of lead
in the barrel
and aid in accuracy.
, zinc
, aluminum or some suitable alloy such as brass
. The bullet that is to be gas checked must be designed for a gas check; there will be a rebated area to allow the cup to fit the base, or a small projection to allow attachment of the check. The check is swage
d onto the bullet, covering most or all of the base; the perimeter is the most important area, so some designs (such as Corbin's Base Guard(tm)) use a short cylindrical projection of the bullet base as a rivet
to lock the check in place. Once assembled, the bullets are loaded normally.
revolver
cartridges or rifle
cartridges, often result in significant problems when coupled with cast
or swaged lead bullets. It was long thought that the high temperatures melted the base of the bullet, but this is no longer thought to be the case. Instead, the high pressures allow propellant gas to escape past the bullet, causing gas cutting, which increases lead deposits in the barrel and unbalances the bullet. A gas check provides a thin layer of harder but still malleable metal on the base of the bullet that obturate
s to provide a seal and prevent the propellant gas leakage that causes gas cutting, and help the bullet grip the rifling
.
While most cartridges operating at such high pressure use jacketed bullets, gas checked bullets are often less expensive, especially to a hand loader
who can recycle lead to make cast bullet
s, and then must only pay for the gas check. Custom lead bullets, such as those for obsolete calibers, wildcat cartridge
s, or for special purposes, are easily made with inexpensive casting or swaging equipment. In contrast, manufacturing jacketed bullets requires far more expensive equipment to draw the jackets and swage in the core, so is generally limited to commercial ammunition producers. As a result, although it is possible for hobbyists to manufacture jacketed bullets, many of them take the easier option and use gas checked bullets instead.
and .357 Magnum
, which were developed from non-magnum cartridges by shooters such as Elmer Keith
. By loading the large capacity cases designed for black powder with large charges of smokeless powder
, velocities well in excess of 1000 ft/s (300 m/s) were produced from handguns for the first time. At these velocities and pressures traditional soft lead bullets would quickly foul the barrel with lead deposits, so gas checked bullets were used in these experimental cartridges.
The other common use of gas checked bullets is in obsolete military rifles. Many of these rifles used calibers that were unique to the rifle; low levels of commercial production and dwindling supplies of surplus ammunition quickly result in high ammunition prices. Many of these rifles use unusual bore diameters; for example, the .303 British
and Soviet 7.62 x 54 R use bore diameters larger than US .30/7.62 mm standard bullets, resulting in a much smaller supply of suitable bullets--often just a single full metal jacket bullet
design in the weight used by the military loading. Custom made bullets also allow the bullet to be carefully sized to match the bore, which can vary considerably in surplus rifles, and provide both more accuracy and more flexibility. Gas checks allow these bullets to be pushed to higher velocities without undue fouling of the barrel and attendant problems.
Ammunition
Ammunition is a generic term derived from the French language la munition which embraced all material used for war , but which in time came to refer specifically to gunpowder and artillery. The collective term for all types of ammunition is munitions...
. Gas checks are used when non-jacketed bullets
Full metal jacket bullet
A full metal jacket is a bullet consisting of a soft core encased in a shell of harder metal, such as gilding metal, cupronickel or less commonly a steel alloy. This shell can extend around all of the bullet, or often just the front and sides with the rear left as exposed lead...
are used in high pressure
Internal ballistics
Internal ballistics, a subfield of ballistics, is the study of a projectile's behavior from the time its propellant's igniter is initiated until it exits the gun barrel...
cartridges
Cartridge (firearms)
A cartridge, also called a round, packages the bullet, gunpowder and primer into a single metallic case precisely made to fit the firing chamber of a firearm. The primer is a small charge of impact-sensitive chemical that may be located at the center of the case head or at its rim . Electrically...
, to prevent the buildup of lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
in the barrel
Gun barrel
A gun barrel is the tube, usually metal, through which a controlled explosion or rapid expansion of gases are released in order to propel a projectile out of the end at a high velocity....
and aid in accuracy.
Construction
Gas checks are most commonly found in the form of a thin cup or disc made of copperCopper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
, zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
, aluminum or some suitable alloy such as brass
Brass
Brass is an alloy of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties.In comparison, bronze is principally an alloy of copper and tin...
. The bullet that is to be gas checked must be designed for a gas check; there will be a rebated area to allow the cup to fit the base, or a small projection to allow attachment of the check. The check is swage
Swage
Swaging is a forging process in which the dimensions of an item are altered using a die or dies, into which the item is forced. Swaging is usually a cold working process; however, it is sometimes done as a hot working process....
d onto the bullet, covering most or all of the base; the perimeter is the most important area, so some designs (such as Corbin's Base Guard(tm)) use a short cylindrical projection of the bullet base as a rivet
Rivet
A rivet is a permanent mechanical fastener. Before being installed a rivet consists of a smooth cylindrical shaft with a head on one end. The end opposite the head is called the buck-tail. On installation the rivet is placed in a punched or pre-drilled hole, and the tail is upset, or bucked A rivet...
to lock the check in place. Once assembled, the bullets are loaded normally.
Why gas checks are needed
High pressures, such as those commonly encountered in maximum loadings of magnumMagnum
Magnum may refer to several things:* Moses Magnum, a Marvel Comics villain*Magnum, P.I., a television series** Thomas Magnum, the lead character...
revolver
Revolver
A revolver is a repeating firearm that has a cylinder containing multiple chambers and at least one barrel for firing. The first revolver ever made was built by Elisha Collier in 1818. The percussion cap revolver was invented by Samuel Colt in 1836. This weapon became known as the Colt Paterson...
cartridges or rifle
Rifle
A rifle is a firearm designed to be fired from the shoulder, with a barrel that has a helical groove or pattern of grooves cut into the barrel walls. The raised areas of the rifling are called "lands," which make contact with the projectile , imparting spin around an axis corresponding to the...
cartridges, often result in significant problems when coupled with cast
Casting
In metalworking, casting involves pouring liquid metal into a mold, which contains a hollow cavity of the desired shape, and then allowing it to cool and solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process...
or swaged lead bullets. It was long thought that the high temperatures melted the base of the bullet, but this is no longer thought to be the case. Instead, the high pressures allow propellant gas to escape past the bullet, causing gas cutting, which increases lead deposits in the barrel and unbalances the bullet. A gas check provides a thin layer of harder but still malleable metal on the base of the bullet that obturate
Obturate
Obturate means to block or obstruct. With reference to firearms and airguns, obturation refers to the process of a bullet or pellet, made of soft material and often with a concave base, flaring under the pressure of firing to seal the bore and engage the barrel's rifling...
s to provide a seal and prevent the propellant gas leakage that causes gas cutting, and help the bullet grip the rifling
Rifling
Rifling is the process of making helical grooves in the barrel of a gun or firearm, which imparts a spin to a projectile around its long axis...
.
While most cartridges operating at such high pressure use jacketed bullets, gas checked bullets are often less expensive, especially to a hand loader
Handloading
Handloading or reloading is the process of loading firearm cartridges or shotgun shells by assembling the individual components , rather than purchasing completely assembled, factory-loaded cartridges...
who can recycle lead to make cast bullet
Cast bullet
A cast bullet is made by allowing molten metal to solidify in a mould. Most cast bullets are made of lead alloyed with tin and antimony; but zinc alloys have been used when lead is scarce, and may be used again in response to concerns about lead toxicity...
s, and then must only pay for the gas check. Custom lead bullets, such as those for obsolete calibers, wildcat cartridge
Wildcat cartridge
A wildcat cartridge, or wildcat, is a custom cartridge for which ammunition and firearms are not mass produced. These cartridges are often created in order to optimize a certain performance characteristic of an existing commercial cartridge.Developing and using wildcat cartridges does not...
s, or for special purposes, are easily made with inexpensive casting or swaging equipment. In contrast, manufacturing jacketed bullets requires far more expensive equipment to draw the jackets and swage in the core, so is generally limited to commercial ammunition producers. As a result, although it is possible for hobbyists to manufacture jacketed bullets, many of them take the easier option and use gas checked bullets instead.
Cartridges commonly using gas checks
The most common use of gas checks is in the .44 Magnum.44 Magnum
The .44 Remington Magnum, or simply .44 Magnum, is a large-bore cartridge originally designed for revolvers. After introduction, it was quickly adopted for carbines and rifles...
and .357 Magnum
.357 Magnum
The .357 S&W Magnum , or simply .357 Magnum, is a revolver cartridge created by Elmer Keith, Phillip B. Sharpe, Colonel D. B. Wesson of firearms manufacturer Smith & Wesson, and Winchester. It is based upon Smith & Wesson's earlier .38 Special cartridge. The .357 Magnum cartridge was introduced in...
, which were developed from non-magnum cartridges by shooters such as Elmer Keith
Elmer Keith
Elmer Keith was an Idaho rancher, firearms enthusiast, and author. Keith was instrumental in the development of the first magnum revolver cartridge, the .357 Magnum, as well as the later .44 Magnum and .41 Magnum cartridges.-Personality and life:Keith's trademarks were his cigars, his ten-gallon...
. By loading the large capacity cases designed for black powder with large charges of smokeless powder
Smokeless powder
Smokeless powder is the name given to a number of propellants used in firearms and artillery which produce negligible smoke when fired, unlike the older gunpowder which they replaced...
, velocities well in excess of 1000 ft/s (300 m/s) were produced from handguns for the first time. At these velocities and pressures traditional soft lead bullets would quickly foul the barrel with lead deposits, so gas checked bullets were used in these experimental cartridges.
The other common use of gas checked bullets is in obsolete military rifles. Many of these rifles used calibers that were unique to the rifle; low levels of commercial production and dwindling supplies of surplus ammunition quickly result in high ammunition prices. Many of these rifles use unusual bore diameters; for example, the .303 British
.303 British
.303 British, or 7.7x56mmR, is a .311 inch calibre rifle and machine gun cartridge first developed in Britain as a blackpowder round put into service in December 1888 for the Lee-Metford rifle, later adapted to use smokeless powders...
and Soviet 7.62 x 54 R use bore diameters larger than US .30/7.62 mm standard bullets, resulting in a much smaller supply of suitable bullets--often just a single full metal jacket bullet
Full metal jacket bullet
A full metal jacket is a bullet consisting of a soft core encased in a shell of harder metal, such as gilding metal, cupronickel or less commonly a steel alloy. This shell can extend around all of the bullet, or often just the front and sides with the rear left as exposed lead...
design in the weight used by the military loading. Custom made bullets also allow the bullet to be carefully sized to match the bore, which can vary considerably in surplus rifles, and provide both more accuracy and more flexibility. Gas checks allow these bullets to be pushed to higher velocities without undue fouling of the barrel and attendant problems.