The rimmed case , also called a flanged case or a rimmed case , has a flange at the base that is larger in diameter than the body of the case. This part, called the rim , plays a fundamental role in positioning the cartridge in the firing chamber and facilitates the extraction of the case after firing.
It is one of the oldest configurations in the history of metallic ammunition, but it is still widely used in revolver cartridges, break-action rifles, lever-action rifles and many hunting ammunition.
What a rimmed case looks like
In the rimmed case, the base ends with a circular lip that is significantly wider than the body. The gun's extractor rests behind this flange to remove the case from the chamber.
The rim can perform two functions simultaneously:
- stop the cartridge at the correct depth in the chamber;
- provide a gripping surface for the extractor or ejector.
The presence of the rim makes the system particularly simple and reliable, especially in weapons in which the cartridges are inserted directly into the chambers, such as revolvers, double-barreled shotguns, over-and-under, express guns and combination guns.
Headspace and cartridge positioning
In rimmed cases , headspace is normally determined by the thickness of the rim. When the cartridge is inserted into the chamber, the front surface of the rim rests on a special recess in the breech.
This stop prevents the cartridge from advancing too far and keeps the base in the correct position relative to the bolt and firing pin.
The system is particularly suitable for cylindrical or slightly tapered cases, which do not have a pronounced shoulder on which to seat the cartridge. In rimless bottleneck cases, however, the headspace is generally determined by the case shoulder.
Extraction in break-action weapons
The rimmed case is particularly suitable for break-action rifles and carbines . When the gun is opened, the extractor can act directly against the rear of the rim, lifting the case from the chamber.
This feature explains the widespread use of flanged cartridges in express double-barreled shotguns and combination rifles. In guns equipped with automatic ejectors, the large surface area provided by the rim also allows for the decisive ejection of the spent case.
For this reason, many European cartridges intended for break-action guns are distinguished by the letter “R” , derived from the German term Rand , meaning edge. Examples of this are the 7×57 R , the 7×65 R , the 8×57 JRS and the 9,3×74 R.
The rimmed case in revolvers
In revolvers, the rim prevents the cartridge from completely passing through the cylinder chamber. When the cylinder is opened, the star-shaped extractor pushes against the rims of all the cartridges simultaneously, allowing the spent cases to be extracted or ejected.
Rimless cartridges can be used in some specially designed revolvers, but often require the use of special moon clips . Rimmed cartridges, on the other hand, function directly with the traditional cylinder extraction system.
Among the best known examples are:
- .38 Special;
- .357 Magnum;
- .44 Magnum;
- .45 Colt;
- .22 Long Rifle.
The rimmed case in rifles
Numerous historical and modern rifle cartridges use a rimmed case. This configuration is common in lever-action guns with tubular magazines, single-shot rifles, and break-action hunting guns.
Among the most representative cartridges we can mention:
- . 30-30 Winchester;
- .45-70 Government;
- .303 British;
- 7,62×54 R;
- 7×65 R;
- 8×57 JRS;
- 9,3×74 R;
- numerous British cartridges named Nitro Express.
Some of this ammunition was created for military bolt-action weapons, others for lever-action rifles or express rifles intended for hunting big game.
Advantages of the rimmed case
- Simple and safe extraction: the rim offers a large gripping surface.
- Well-defined headspace: the cartridge is stopped by the rim without depending on the shoulder or collar.
- Reliability in break-action weapons: It is particularly suitable for double-barreled, express, combined and single-shot guns.
- Natural functioning in revolvers: The rim holds the cartridge in the cylinder and allows for the simultaneous extraction of the cases.
- Adaptability to cylindrical cases: It can also be used when a sufficiently pronounced shoulder is missing.
Rimmed Case Limits
The protruding flange can create difficulties when stacking cartridges inside a magazine. If the rim of the top cartridge is positioned behind that of the cartridge below, rim lock can occur , which prevents proper feeding.
To avoid this problem, magazines intended for rimmed ammunition must be designed to maintain the rims in the correct position. The top cartridge must be positioned with its rim in front of the rim of the cartridge below it.
Compared to rimless cases, rimmed ones are generally less suitable for modern high-capacity double-stack magazines and semi-automatic weapons. However, there are numerous exceptions, especially among historic military weapons and some hunting rifles.
Difference between rimmed and rimless
In a rimmed case , the rim clearly protrudes beyond the diameter of the body. In a rimless case , despite the name, the base is still present, but its diameter is essentially the same as that of the body of the case. The extractor fits into a groove machined in front of the base.
Rimless cases promote a more linear feeding from magazines and are therefore very common in semi-automatic pistols and modern bolt-action or semi-automatic rifles.
There are also intermediate or different configurations:
- semi-rimmed: hem slightly wider than the body;
- rebated rim: case back with a smaller diameter than the body;
- belted: case equipped with a reinforcing belt and positioning close to the base.
Rimmed and rimfire do not mean the same thing
The terms rimmed and rimfire refer to two different characteristics. Rimmed describes the shape of the base, while rimfire refers to the cartridge's ignition system.
In a rimfire cartridge, such as the .22 Long Rifle, the primer mixture is distributed inside the rim and is activated by the crushing force of the firing pin. A centerfire cartridge can also be rimmed, but uses a primer placed in the center of the base.
The .22 Long Rifle is therefore simultaneously rimmed and rimfire, while cartridges such as .357 Magnum, .30-30 Winchester and 9,3×74 R are rimmed but at central percussion.
Smoothbore shotgun shells
Smoothbore shotgun shells also typically feature a flanged base. The rim holds the cartridge in the chamber and allows the extractor or ejector to remove it after firing.
This principle is used in break-action rifles as well as in semi-automatic and pump-action shotguns. The particular structure of shotshells, however, is generally treated separately from the classification of metal cases for rifled weapons.
Final houghts
The rimmed case represents a simple, robust, and still highly relevant solution. The protruding flange ensures precise seating of the cartridge and makes extraction particularly reliable in break-action guns and revolvers.
Its main limitation is magazine feeding, where the overlapping rims require specific design. For this reason, rimless cases dominate in modern repeating and semi-automatic weapons, while rimmed ones continue to be a preferred choice for revolvers, express rifles, combination guns, single-shot rifles, and many traditional hunting cartridges.
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