.30 Carbine

In the late 1930s the US Army began lobbying for a new ‘light rifle’ or carbine to be issued to support troops for whom their personal weapon wasn’t their primary concern.   It was not until 1941 that Ordnance Department’s the Light Rifle Trials began seeking a new carbine.  However, by that time the rifle’s cartridge had been chosen.

The light rifle was intended to bridge the gap between the .30-06 chambered M1 Garand battle rifle and the M1911 pistol in .45ACP - which was frequently issued to support troops as their main defensive sidearm.  The new rifle would need a cartridge which was accurate and hard hitting but not as large as the .30-06 round.  
The .30 Carbine round had its origins in a much older Winchester cartridge the .32 Winchester Self-Loading round which had initially be developed for the Winchester Model 1905 self loading rifle. 

The .32 Winchester Self Loading (.32WSL) has a slightly heavier bullet weighing 165 grains to the .30 Carbine’s 110gr.  The .32WSL has a shorter case as a result the Carbine round had a higher muzzle velocity leaving the barrel at 1,900 feet per second.  This increased velocity was also the result of increased power from newer chemical propellants than its parent cartridge.  The case itself is straight and rimless, unlike other contemporary rifle ammunition it is neither necked nor is the projectile pointed like a conventional spitzer bullet.  The new ammunition went into production in February 1941, as the Ball Cartridge Carbine Caliber .30 SL, M1.

The .30 Carbine’s parent cartridge the .32 Winchester Self-Loading Cartridge (source)

The light rifle selected was a design from Winchester, adopted in October 1941, as the M1 Carbine.  It chambered the new round making it a light, handy rifle with light recoil which meant it was easy to shoot and ideal for troops who were specialists and did not have the time for full marksmanship training.  It proved to be an excellent intermediate between the M1 Garand and the M1911, so much so that it was increasingly issued to squad leaders and officers. However, it was noted by troops fighting in the Pacific Theatre that the round did not penetrate dense jungle well. Similarly, later during the Korean War there were numerous after-action reports noting the lack of stoping power of the .30 Carbine round even at close quarters. This was due to its ball projectile and lower velocity than a full-sized .30 calibre round.

While the .30 Carbine cartridge could be described as an intermediate round, it is not in the same category as the German 7.92mm Kurz - a true intermediate calibre which maximised power and accuracy while minimising size and weight.  

Source:

Image One Source

Image Two & Three from Popular Science, June 1942 (source)

The Greenhill Military Small Arms Data Book, I.V. Hogg, (1999)

Military Small Arms of the 2oth Century, I.V. Hogg & J. Weeks, (1985)