The US .30 cal M1 Carbine is one of the most important developments in the personal defense weapon story, being one of the very first* intermediate calibers to be adopted as standard issue by a nation, and arguably the first purpose-designed PDW caliber in history. Even today it occupies a strange halfway point between pistol and rifle cartridges, being similar in design to a long pistol round or magnum revolver round with its straight-walled case and round-nosed bullet, but loaded with rifle powders designed for the 18″ barrel of the handy little M1 Carbine.
*I have mentioned before that it is in fact the Italians who claimed the prize of “first intermediate caliber to be adopted as standard issue”, with their long but still very much intermediate 7.35x51mm round.
The .30 Carbine is so weird in part because it’s descended from an innovative and influential but little-known family of rounds developed by Winchester in the early 1900s. These were the Winchester Self-Loading (WSL) rounds, including .32 WSL, .35 WSL, .351 WSL, and .401 WSL. Each round was a straight-walled, semi-rimmed cartridge firing a round-nosed bullet at modest pressure, just like the .30 Carbine. This design allowed the use of a simple blowback action, shared between the Winchester 1905, 1907, and 1910 rifles.
When Winchester was asked by Ordnance to develop a round for a new echelon weapon to complement the .45 cal 1911 handgun, their engineers fell back to the basic design of these rounds, adapting the .32 WSL into what was called in development the .30 SL, virtually identical to today’s .30 Carbine. The .30 SL was an entirely conservative design, which hastened development considerably. Even though Winchester developed a round suitable for straight blowback actions, the rifle they eventually submitted – designed by William Roemer and Fred Humeston, and based on the work done by convict David Marshall Williams – was a gas-operated, locked breech design. Still, the mild working characteristics of the .30 SL allowed the design of a very lightweight and simple gun, in a similar fashion to how the blowback-friendly .32 and .380 ACP rounds allowed the Kel-Tec P-32 and P3AT to be much smaller and lighter than their blowback counterparts.
Still, the .30 Carbine is a round that has taken considerable criticism for its lack of performance, so it’s worthwhile to take a look at exactly how it does in comparison to other rounds used for the same purpose:
Here we see pretty much exactly what we’d expect: A round that starts out quite admirably thanks to its good velocity and energy, but which tends to underperform at range due to its dumpy ballistic coefficient.
Weight-wise, the .30 Carbine is also a bit of a disappointment, clocking in at 12.70 grams per round of M2 .30 Carbine Ball ammunition, heavier than the far more capable 5.56×45.
Overall, the .30 Carbine is a round that is historically important, but not terribly ballistically relevant to the modern discussion of personal defense weapon ammunition. Any series covering this topic would be incomplete without a look at the round, however!