Cartridge cases are designed for gun loading. Case design uses the rim style to help clarify cartridges. Rimmed have the flange, traditionally found in revolver cartridges and ammo for the lever action and single and double shot barrels. Semi-Rimmed is just a smaller rim. Rimless the head is the same diameter as the case base, rebated the rim and extraction groove is smaller in diameter base. Rimmed and semi-rimmed are great for revolvers, singe shot break open single and double barrel sporting weapons and provide the for a positive head space but they aren’t ideal for bolt and autoloading actions. The last is the belted magnums with the belt allowing efficient bolt action feed with the positive head spacing of the rimmed cartridges and identifies the cartridge of a powerful magnum.
Straight Walled VS Bottleneck Cartridges
The other descriptive factor is the case. Straight or slightly tapered vs. bottleneck cartridges. Rimmed cartridges are commonly a straight sided cartridge case where rimless are generally bottlenecked cartridges. Modern cartridges tend to be named after the cartridge designer or manufacturer. Guns are named after the designer and manufacturer(s) as well. The 30-06 Springfield combines the designer, the caliber and year of adoption. The 30-30 Winchester was designed near the end of the black powder era and was supposed to be .30 caliber with 30 grains of smokeless powder. The 30-40 uses the same system, just boosting the smokeless charge to 40 grains of nitrocellulose based powder. Both sported rimmed bottlenecked cases. A lot of hype and commercial exploitation is also present. The 38 Special was named to distinguish it from the other 38 caliber pistol rounds. The 357 Magnum was developed from the 38 but is longer to prevent it being loaded in older 38 Special chambers, due to its higher pressures. Savage introduce the .250-3000 in 1915. At 25 caliber the round could exceed 3000 fps at the muzzle with an 87-grain bullet, a big deal in the early 20th century.
There are many interesting histories in cartridge and gun developments, particularly in how they come to be named. We haven’t even scratched the surface if one was to investigate wild cats. The 35 Whelen is a 30-06 blown out to accept 35 caliber bullets. The 338-378 Weatherby is the 378 Weatherby magnum reduce to 338 caliber bullets. P.O. Ackley improved many rounds by reducing case taper and pushing neck taper forward increasing the powder capacity. The 300 Blackout and 300 Whisper only vary in chamber specs. When the 10mm Auto (10x25mm) was introduced is was not acceptable to many shooters because of the recoil and muzzle blast. Shorten the case to 22mm and we have the 10x22mm also known as the 40 S&W. Bottle neck the 40 S&W down to 9mm and we have the 357 Sig. Colt introduced the 1911 pistol, in 1911 with the .45ACP (automatic Colt pistol) cartridge, in Europe it is the 11.23x23mm. The British us flanged for rimmed and produce the same cartridges in rimmed for double hunting rifles or rimless for the bolt action crowd.