A rim is an external flange that is machined, cast, molded, stamped or pressed around the bottom of a firearms 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 the cartridge
1.1 Rimmed 1.2 Rimless 1.3 Semi-rimmed 1.4 Rebated rim 1.5 Belted
2 See also 3 References
Types There are various types of firearms rims in use in modern ammunition. These types are rimmed, rimless, semi-rimmed, rebated rim, and belted. These categories describe the size of the rim in relation to the base of the case.
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
cartridges in a
Rimless 9mm Parabellum pistol cartridges
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 box magazine, although they also work well in belt,
drum 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 moon clip (for example, the Colt or Smith & Wesson
M1917 revolvers in .45ACP).
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 hold 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
of accuracy. This is not an issue for break-action single shot
firearms, for obvious reasons, although it could potentially cause
problems in double rifles or "drilling"-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 9mm Parabellum, .40
S&W, and .45 ACP. Rimless rifle examples include the .223
Remington, .308 Winchester,
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, a higher pressure loading of the old
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, the rebated rim provides some
additional benefits when considered in conjunction with other
One example of a rebated rim cartridge is the
.50 Action Express
Belted .375 H&H Magnum (Left) .338 Winchester Magnum (Right) US Quarter (24 mm) for scale
The original purpose of the "belt" on belted cases (often referred to
as belted magnums) 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 charges
instead of modern smokeless powder.
List of handgun cartridges List of rifle cartridges Table of handgun and rifle cartridges
^ House, James E (21 October 2016). Gun Digest Book of .22 Rimfire. "F+W Media, Inc.". pp. 9–11. ISBN 978-1-4402-4659-3. ^ Woodard, Todd (1 October 2011). Shooter's Bible Guide to Cartridges. NY: Skyhorse Pub. pp. 11–16. ISBN 978-1-61608-222-2. ^ a b c d e Walker, Robert E. (21 March 2013). Cartridges and Firearm Identification. CRC Press. pp. 100–101. ISBN 978-1-4665-8881-3. ^ Sweeney, Patrick (1 October 2001). The Gun Digest Book of the 1911. Iola, Wisconsin: Gun Digest Books. pp. 53–55. ISBN 0-87349-281-1. ^ Fitzpatrick, Brad (17 November 2015). Handgun Buyer's Guide: A Complete Manual to Buying and Owning a Personal Firearm. New York: Skyhorse Publishing Company, Incorporated. pp. 368–369. ISBN 978-1-63450-966-4. ^ a b Woodard, W. Todd (24 October 2016). "Cartridge Identification". Cartridges of the World: A Complete and Illustrated Reference for Over 1500 Cartridges. Iola, Wisconsin: "F+W Media, Inc.". pp. 14–15. ISBN 978-1-4402-4642-5. ^ a b Massaro, Philip P. (11 September 2014). Gun Digest Shooter's Guide to Reloading. Iola, Wisconsin: F+W Media. pp. 31–32. ISBN 978-1-4402-3998-4. ^ Sweeney, Patrick (13 February 2014). Gunsmithing - The AR-15. Iola, Wisconsin: Krause Publications. p. 84. ISBN 978-1-4402-3848-2. ^ Lee, Jerry (12 August 2016). Gun Digest 2017. Iola, Wisconsin: "F+W Media, Inc.". p. 115. ISBN 978-1-4402-4658-6.
Ackley, P.O. (1927) . Handbook for Shooters & Reloaders. vol I (12th Printing ed.). Salt Lake City, Utah: Plaza Publishing. pp. 197–202. ISBN 978-99