A rim is an external

flange A flange is a protruded ridge, lip or rim (wheel), rim, either external or internal, that serves to increase shear strength, strength (as the flange of an iron beam (structure), beam such as an I-beam or a T-beam); for easy attachment/transfer of ...

that is machined, cast, molded, stamped, or pressed around the bottom of a

firearm A firearm is any type of gun designed to be readily carried and used by an individual. The term is legally defined further in different countries (see Legal definitions). The first firearms originated in 10th-century China, when bamboo tubes ...

s cartridge. Thus, rimmed cartridges are sometimes called "flanged" cartridges. Almost all cartridges feature an extractor or headspacing rim, in spite of the fact that some cartridges are known as "rimless cartridges". The rim may serve a number of purposes, including providing a lip for the extractor to engage, and sometimes serving to

headspace Headspace may refer to: * Headspace (company), an online healthcare company specializing in meditation * Headspace (organisation), an Australian non-profit organization for youth mental health *Headspace or ullage, the unfilled space in a contain ...

the cartridge.

Types

There are various types of firearms rims in use in modern ammunition. The main types are categorized as rimmed, rimless, semi-rimmed, rebated rim, and belted. These describe the size of the rim in relation to the base of the case.

Rimmed

The rimmed cartridge, sometimes called flanged cartridge, is the oldest of the types and has a rim that is significantly larger in diameter than the base of the cartridge. Rimmed cartridges use the rim to hold the cartridge in the chamber of the firearm, with the rim serving to hold the cartridge at the proper depth in the chamber—this function is called " headspacing". Because the rimmed cartridge headspaces on the rim, the case length is of less importance than with rimless cartridges. This allows some firearms chambered for similar rimmed cartridges to safely chamber and fire shorter cartridges, such as using

.38 Special The .38 Special, also commonly known as .38 S&W Special (not to be confused with .38 S&W), .38 Smith & Wesson Special, .38 Spl, .38 Spc, (pronounced "thirty-eight special"), or 9x29mmR is a rimmed, centerfire cartridge designed by Smith & ...

cartridges in a

.357 Magnum The .357 Smith & Wesson Magnum, .357 S&W Magnum, .357 Magnum, or 9×33mmR as it is known in unofficial metric designation, is a smokeless powder cartridge with a bullet diameter. It was created by Elmer Keith, Phillip B. Sharpe, and Douglas B. ...

revolver - as these are the same diameter despite the nomenclature. Rimmed cartridges are well suited for certain types of actions, such as

revolver A revolver (also called a wheel gun) is a repeating handgun that has at least one barrel and uses a revolving cylinder containing multiple chambers (each holding a single cartridge) for firing. Because most revolver models hold up to six r ...

s and

break-action Break action is a type of firearm action in which the barrel or barrels are hinged much like a door and rotate perpendicularly to the bore axis to expose the breech and allow loading and unloading of cartridges. A separate operation may be requir ...

firearms, where the rim helps hold the cartridge in position. Rimmed cartridges generally do not work quite as well in firearms that feed from a

box magazine A magazine is an ammunition storage and feeding device for a repeating firearm, either integral within the gun (internal/fixed magazine) or externally attached (detachable magazine). The magazine functions by holding several cartridges withi ...

, since the magazine must be carefully loaded so that the rim from each successive case is loaded ahead of the round beneath it, so the round will not snag on the rim of the cartridge below it as the bolt strips it out of the magazine. However, box magazine firearms firing rimmed cases have seen extensive use; the famous

Lee–Enfield The Lee–Enfield or Enfield is a bolt-action, magazine-fed repeating rifle that served as the main firearm of the military forces of the British Empire and Commonwealth during the first half of the 20th century, and was the British Army's sta ...

rifle used by the UK, and the Russian Mosin-Nagant rifle which uses an interrupter to help prevent the snags, were both used from before World War I until after World War II. Semi-automatic handguns have been chambered in rimmed cartridges as well, for example a LAR Grizzly or

Desert Eagle The Desert Eagle is a gas-operated, semi-automatic pistol known for chambering the .50 Action Express, the largest centerfire cartridge of any magazine-fed, self-loading pistol. Magnum Research Inc. (MRI) designed and developed the Desert Eagle ...

or .44 Magnum. And, of course, the

.22 Long Rifle The .22 Long Rifle or simply .22 LR or 22 (metric designation: 5.6×15mmR) is a long-established variety of .22 caliber rimfire ammunition originating from the United States. It is used in a wide range of rifles, pistols, revolvers, smo ...

is extremely popular in semi-automatics. Some types of rimmed cartridges, such as rimfire cartridges, also use the rim to contain the priming compound used to ignite the cartridge instead of a centrally-mounted primer such as used in

centerfire Two rounds of .357 Magnum, a centerfire cartridge; notice the circular primer in the center A centerfire cartridge is a firearm metallic cartridge whose primer is located at the center of the base of its casing (i.e. "case head"). Unlike rimf ...

cartridges. Under the

metric Metric or metrical may refer to: * Metric system, an internationally adopted decimal system of measurement * An adjective indicating relation to measurement in general, or a noun describing a specific type of measurement Mathematics In mathema ...

cartridge designation system, a capitalized "R" added at the end of the designation denotes a rimmed cartridge. For example, " 7.62×54mmR" is a rimmed cartridge, while " 7.62×51mm" is a rimless cartridge. Under Imperial designations, there is typically no distinction between rimmed and unrimmed cartridges, unless one is referring to a rimmed version of a cartridge which is typically rimless, such as the .45 Auto Rim, a special rimmed version of the

.45 ACP The .45 ACP ( Automatic Colt Pistol) or .45 Auto (11.43×23mm) is a rimless straight-walled handgun cartridge designed by John Moses Browning in 1904, for use in his prototype Colt semi-automatic pistol. After successful military trials, it ...

("Automatic Colt Pistol" aka ".45 Auto"), intended for use in M1917 service revolvers. Examples of rimmed handgun cartridges include the

.44 Special The .44 Smith & Wesson Special, also commonly known as .44 S&W Special, .44 Special, .44 Spl, .44 Spc, (pronounced "forty-four special"), or 10.9x29mmR is a smokeless powder center fire metallic revolver cartridge developed by Smith & Wesson in 1 ...

, .44 Magnum,

.45 Schofield The .45 Schofield, also referred to as .45 Smith & Wesson is a revolver cartridge developed by Smith & Wesson for their S&W Model 3 Schofield top-break revolver. It is similar to the .45 Colt round though shorter and with a slightly larger ri ...

, and .45 Colt. Rimmed rifle cartridge examples include the .22 Hornet,

.30-30 Winchester The .30-30 Winchester/.30 Winchester Center Fire cartridge was first marketed in 1895 for the Winchester Model 1894 lever-action rifle.7.62×54mmR,

.303 British The .303 British (designated as the 303 British by the C.I.P. and SAAMI) or 7.7×56mmR, is a calibre rimmed rifle cartridge. The .303 inch bore diameter is measured between rifling lands as is the common practice in Europe which follows th ...

, 8×50mmR Lebel, and .45-70 Government.

Rimless

On a "rimless" case, the rim has almost or exactly the same diameter as the base of the case; the recess formed between the rim and the body of the cartridge is known as an '' extractor groove'', since it forms a lip which can be grasped by an ''extractor'' to extract the empty case after being fired. Since there is no rim projecting past the edge of the case, the cartridge must headspace on the case mouth, for a straight walled case, or on the case's shoulder for a bottlenecked case (although a bottlenecked case ''can'' headspace on the case mouth, depending on the cartridge); the extractor groove serves only for extraction. The lack of a projecting rim makes rimless cases feed very smoothly from box magazines, and they are primarily used in firearms that feed from a

, although they also work well in belt,

drum The drum is a member of the percussion group of musical instruments. In the Hornbostel-Sachs classification system, it is a membranophone. Drums consist of at least one membrane, called a drumhead or drum skin, that is stretched over a sh ...

and tube-fed weapons. Rimless cases are not well suited to break-open and revolver actions, though they can be used with appropriate modifications, such as a spring-loaded extractor or, in a revolver, a half or full moon clip (for example, the Colt or Smith & Wesson M1917 revolvers in

). Since a straight-walled rimless cartridge is designed to headspace off of the case mouth, this prevents the ammunition loader or manufacturer from using a heavy crimp, which is a ring pinched or "crimped" into the cartridge case, designed to lock the bullet securely in place until fired. Crimping affects the overall length of the cartridge, and thus cannot be used on cartridges which headspace on the case mouth. This can be a problem for magnum revolvers or rifles which simultaneously chamber more than one round of ammunition, as the recoil from the firing successive rounds can loosen the bullets in the remaining cartridges, and cause their bullet seating depth to change, which can have a serious effect on accuracy, or could, in the case of a revolver, cause a bullet to protrude sufficiently from the front of the cylinder to obstruct the revolving of the cylinder thus jamming the gun from firing additional rounds. This is not an issue for

''single shot'' firearms, for obvious reasons, although it could potentially cause accuracy (but not jamming) problems in double rifles or "

drilling Drilling is a cutting process where a drill bit is spun to cut a hole of circular cross-section in solid materials. The drill bit is usually a rotary cutting tool, often multi-point. The bit is pressed against the work-piece and rotated at ...

"-type big game rifles, provided they have more than one rifle barrel (some "drillings" are made with three or more rifle barrels, without any shotgun component). Examples of rimless handgun cartridges include the

.380 ACP The .380 ACP (9×17mm) ( Automatic Colt Pistol) is a rimless, straight-walled pistol cartridge developed by firearms designer John Moses Browning. The cartridge headspaces on the mouth of the case.Wilson, R. K. ''Textbook of Automatic Pisto ...

, 9mm Parabellum,

.357 SIG The .357 SIG (designated as the 357 Sig by the SAAMI and 357 SIG by the C.I.P. or 9×22mm in unofficial metric notation) is a bottlenecked rimless centerfire handgun cartridge developed by the Swiss- German firearms manufacturer SIG Sauer, ...

, .40 S&W,

10mm Auto The 10mm Auto (10×25mm, official C.I.P. nomenclature: 10 mm Auto, official SAAMI nomenclature: 10mm Automatic) is a semi-automatic pistol cartridge introduced in 1983. Its design was adopted and later produced by ammunition manufacturer ...

.45 GAP The .45 GAP (Glock Auto Pistol) or .45 Glock (11.43×19mm) is a pistol cartridge designed by Ernest Durham, an engineer with CCI/Speer, at the request of firearms manufacturer Glock to provide a cartridge that would equal the power of the ...

, and

. Rimless rifle examples include the

.223 Remington The .223 Remington (designated as the 223 Remington by the SAAMI and 223 Rem by the CIP) is a rimless, bottlenecked rifle cartridge. It was developed in 1957 by Remington Arms and Fairchild Industries for the U.S. Continental Army Command ...

, 6.5x52mm Carcano, 6.5×54mm Mannlicher–Schönauer, 6.5×55mm Swedish,

.308 Winchester The .308 Winchester is a smokeless powder rimless bottlenecked rifle cartridge widely used for hunting, target shooting, police, military, and personal protection applications globally. It is similar but not identical to the 7.62×51mm NATO ...

.30-06 Springfield The .30-06 Springfield cartridge (pronounced "thirty- aught-six" ), 7.62×63mm in metric notation, and called the .30 Gov't '06 by Winchester, was introduced to the United States Army in 1906 and later standardized; it remained in military use ...

, and 7.92×57mm Mauser.

Semi-rimmed

On a semi-rimmed case the rim projects slightly beyond the base of the case, though not as much as a rimmed cartridge. The tiny rim provides minimal interference feeding from a box magazine, while still providing enough surface to headspace on. Semi-rimmed cases are less common than the other types. The

.38 Super The .38 Super, also known as .38 Super +P, .38 Super Auto, .38 Super Automatic, .38 Super Automatic +P, or 9×23mmSR, is a pistol cartridge that fires a bullet. It was introduced in the late 1920s as a higher pressure loading of the .38 ACP, a ...

, a higher pressure loading of the old .38 ACP case, is notorious for being less accurate than rimless cases, and so most modern .38 Super handguns are chambered so that the cartridge headspaces off the case mouth, like a rimless case. If the chamber is cut shallow, so the case headspaces off the mouth, the rim is used for extraction only; a standard chamber will use the rim for both headspacing and extraction. Examples of semi-rimmed handgun cartridges are

.25 ACP The .25 ACP ( Automatic Colt Pistol) (6.35×16mmSR) is a semi-rimmed, straight-walled centerfire pistol cartridge introduced by John Browning John Moses Browning (January 23, 1855 – November 26, 1926) was an American firearm designe ...

, .32 ACP, 8x22mm Nambu,

.38 ACP The .38 ACP ( Automatic Colt Pistol), also known as the .38 Auto or 9x23mmSR, is a semi-rimmed pistol cartridge that was introduced at the turn of the 20th century for the John Browning-designed Colt M1900. It was first used in Colt's Model ...

, and

9mm Browning Long The 9mm Browning Long x 20mm SR'' is a military centerfire pistol cartridge developed in 1903 for the FN Model 1903 adopted by Belgium, France, Estonia, the Netherlands, and Sweden.Janson, O"Browning pistol M1903 becomes Swedish Pistol m/1907 ...

. Semi-rimmed rifle examples include the .220 Swift, .280 Ross, 6.5×50mm Arisaka, .308 Marlin Express, .338 Marlin Express, and .444 Marlin.

Rebated rim

Rebated rim cartridges have a rim that is significantly smaller in diameter than the base of the case, serving only for extraction. Functionally the same as a rimless case, a rebated rim allows a gun to be easily converted to fire a larger-than-normal cartridge, as most of a gun's

action Action may refer to: * Action (narrative), a literary mode * Action fiction, a type of genre fiction * Action game, a genre of video game Film * Action film, a genre of film * ''Action'' (1921 film), a film by John Ford * ''Action'' (1980 fil ...

(loading/extraction mechanism) does not need to be altered as long as the rim size is preserved. One example of a rebated rim cartridge is the

.50 Action Express The .50 Action Express (AE, 12.7×33mmRB) is a large- caliber handgun cartridge, best known for its usage in the Desert Eagle. Developed in 1988 by American Evan Whildin of Action Arms, the .50 AE is one of the most powerful pistol cartridge ...

(or .50 AE), commonly chambered in the

pistol. In order to simplify production, and to decrease the cost of ownership, the .50 AE was designed with a rebated rim which matched the diameter of the rim of the .44 Magnum, the most common caliber used in the Desert Eagle. By using the same rim dimensions, a Desert Eagle could be converted from .44 Magnum to .50 AE by merely changing the

barrel A barrel or cask is a hollow cylindrical container with a bulging center, longer than it is wide. They are traditionally made of wooden staves and bound by wooden or metal hoops. The word vat is often used for large containers for liquids, u ...

and magazine. Other convertible cartridges, such as the short-lived .41 Action Express (with the same rim diameter as

9×19mm Parabellum The 9×19mm Parabellum (also known as 9mm Parabellum or 9mm Luger or simply 9mm) is a rimless, tapered firearms cartridge. Originally designed by Austrian firearm designer Georg Luger in 1901, it is widely considered the most popular handgu ...

) used in the

Jericho 941 The Jericho 941 is a double-action/single-action semi-automatic pistol developed by Israel Military Industries (now Israel Weapon Industries) introduced in 1990. It was first imported into the United States in 1990 by K.B.I., Inc. of Harrisbur ...

convertible pistol and Uzi submachine gun and carbine, would function in the same magazine, and thus required only a barrel change to change caliber. The .440 Cor-Bon is another cartridge with a rebated rim the same size as a .44 Magnum. The FN 5.7x28mm (used in the FN Five-seveN semi-automatic handgun and

FN P90 The FN P90 is a compact 5.7×28mm personal defense weapon designed and manufactured by FN Herstal in Belgium. It can also be considered a submachine gun. Created in response to NATO requests for a replacement for 9×19mm Parabellum firearms, t ...

personal defense weapon) is a well-known cartridge with a slightly rebated rim, but the reason for the choice is not clear, as there is no other cartridge which it is compatible with. The recent (early 2000s)

Winchester Short Magnum Winchester Short Magnum, or WSM, refers to a family of rebated rim bottlenecked centerfire short magnum cartridges developed in the early 2000s by the U.S. Repeating Arms Company, the maker of Winchester rifles and one of the oldest firearms man ...

, Winchester Super Short Magnum, Remington Ultra Magnum and Remington Short Action Ultra Magnum families of rifle cartridges also feature rebated rims. All of these cases were based on the

.404 Jeffery The .404 Jeffery is a rifle cartridge designed for hunting large, dangerous game animals, such as the " Big Five" (elephant, rhino, cape buffalo, lion and leopard) of Africa. The cartridge is standardized by the C.I.P. and is also known as .404 ...

with the rim reduced from .543 inches to fit the .532 inch bolt face for existing magnum rifles. The

.50 Beowulf The .50 Beowulf is a 12mm caliber rifle cartridge developed by Bill Alexander of Alexander Arms for use in an AR-15 rifle. Design and specifications The cartridge utilizes a rebated rim, sized to match the rim of the 6.5mm Grendel round. The ...

rifle cartridge uses a rebated rim design. This round is used in specialized

AR-15 An AR-15-style rifle is any lightweight semi-automatic rifle based on the Colt AR-15 design. The original ArmaLite AR-15 is a scaled-down derivative of Eugene Stoner's ArmaLite AR-10 design. The then Fairchild Engine and Airplane Corporatio ...

upper receivers, and the rim matches the size of the rim of the 7.62×39mm, allowing those parts to be used in the custom-built upper receivers. Other rebated rimmed rifle examples include the

.450 Bushmaster The .450 Bushmaster is a rifle cartridge developed by Tim LeGendre of LeMag Firearms, and licensed to Bushmaster Firearms International. The .450 Bushmaster is designed to be used in standard M16s and AR-15s, using modified magazines and u ...

.458 SOCOM The .458 SOCOM (11.63×40mm) is a moderately large round designed to work in an AR-15 platform. This is achieved by installing a 458 bolt and barrel. The round offers a supersonic muzzle velocity of and , similar to a light .45-70 but with a m ...

.500 Jeffery The .500 Jeffery is a big-game rifle cartridge that first appeared around 1920, and was originally introduced by the August Schuler Company, a German firm, under the European designation "12.7×70mm Schuler" or ".500 Schuler". When offered by th ...

, and .375 SWISS P. Rebated rims are used for a different reason on cartridges of automatic cannons derived from the 20-mm Becker, of which the best known belong to the Oerlikon family. These "advanced primer ignition" (API) blowback weapons feature straight-sided chambers which are longer than necessary to contain the case. The face of the bolt has the same diameter as the case and follows it into the chamber. This means that the extraction claw also has to fit within the chamber, and therefore the case has a rebated rim.

Belted

The original purpose of the "belt" on belted cases (often referred to as

belted magnum The term belted magnum or belted case refers to any cartridge, but generally a rifle cartridge, with a shell casing that has a pronounced "belt" around its base that continues 2–4 mm past the extractor groove. This design originated with the B ...

s) was to provide headspacing; the extractor groove is cut into the belt just as it is cut into the case head on a rimless case. The belt acts as a rim on what is essentially a rimless case. The design originated in England around 1910 with the .400/375 Belted Nitro Express (also known as the .375/.400 Holland & Holland, and .375 Velopex). The addition of the belt allowed the cartridge to properly headspace, despite the relative lack of a definite shoulder. The reason for the lack of a definitive shoulder was that these old British cartridge cases were intended for firing

cordite Cordite is a family of smokeless propellants developed and produced in the United Kingdom since 1889 to replace black powder as a military propellant. Like modern gunpowder, cordite is classified as a low explosive because of its slow burni ...

charges instead of modern

smokeless powder Finnish smokeless powderSmokeless powder is a type of propellant used in firearms and artillery that produces less smoke and less fouling when fired compared to gunpowder ("black powder"). The combustion products are mainly gaseous, compared to ...

. Cordite was extruded as

spaghetti Spaghetti () is a long, thin, solid, cylindrical pasta.spaghetti
Dictionary.com. Dictionary.com Unabridg ...

-like rods, so the cartridge cases had to be fairly cylindrical shaped to accommodate the cordite propellant rods. The belt was carried through on other cartridges derived from the .375 Velopex, like the belted .375 Holland & Holland Magnum of 1912, in some cases to allow the cartridge to function in bolt-action rifles (the original .375 H&H Magnum was a rimmed case for use in double-barreled rifles), or to prevent the higher-pressure magnum cartridge from accidentally being chambered in a gun with a chamber of similar size. Examples of belted handgun cartridges include the .40 BSA Auto Pistol and .40 G&A Magnum. Belted rifle examples include the .224 Weatherby Magnum,

.300 Winchester Magnum The .300 Winchester Magnum (also known as .300 Win Mag or .300 WM) (7.62×67mmB, 7.62x66BR) is a belted, bottlenecked magnum rifle cartridge that was introduced by the Winchester Repeating Arms Company in 1963. The .300 Winchester Magnum is a m ...

, .375 H&H Magnum,

.450 Marlin The .450 Marlin is a firearms cartridge designed as a modernized equivalent to the .45-70 cartridge. It was designed by a joint team of Marlin and Hornady engineers headed by Hornady's Mitch Mittelstaedt, and was released in 2000, with cartri ...

.458 Lott The .458 Lott is a .458 caliber rifle cartridge designed for the purpose of hunting large, thick-skinned dangerous game animals in Africa. It is based on the full length .375 H&H Magnum case blown out and shortened to . The .458 Lott was des ...

, and

.55 Boys The .55 Boys (13.9×99mmB in metric) is an anti-tank cartridge used by the United Kingdom in World War II. It was designed for use with the Boys Anti-Tank Rifle. Design The .55 Boys is a 13.2×99mm Hotchkiss cartridge necked up to accept a .5 ...

. In the United States, the belt became somewhat synonymous with "magnum" during the late 20th century. More recently, new "magnum" cartridges introduced in the United States have been rimless or used rebated rims based on the

that fit the same .512" bolt face used for the belted cases.

References

* {{DEFAULTSORT:Rim (Firearms) Ammunition

Types

Rimmed

Rimless

Semi-rimmed

Rebated rim

Belted

See also

References