Between the world wars, both the US and the British where contemplating .280 (7mm) rifles. The British round would have been a great assault rifle cartridge and the US development would have fed the M1 Garand. Both powers recognized the fact that the vast majority of combat occurred at ranges under 300-350 yards and that the .30 caliber cartridges of the day where much two powerful for realistic combat. The 7.62x54R Russian, .303 British, 7.9x57mm Mauser and the 30-06 of the US were to powerful for the infantry. But because of the stocks of ammo in the US arsenals, and the entry of the British into World War II in the late 30’s the 7mm rounds never happened.
The US introduced the .30 Carbine as a replacement for sidearms for officers and other personnel needing a defensive weapon and considered the carbine to be more effective than the 1911 45 ACP sidearm. The .30 carbine round is based on the .32 Winchester self-Loading and pushes a .308 110 grain bullet to about 1990 fps. Two handed operation made it more effective as far as accuracy, and because of its 15 to 30 round magazines offered superior fire power to the 1911 sidearm. Light weight and popular, it was not a proven man killer but for its military use it was effective.
16.5” Barreled Carbine Fed By Glock Magazines in 10mm
Over the years various manufacturers have introduced pistol caliber carbines in various calibers, primarily 9mm, .40 S&W and .45 Colt Automatic. But on closer inspection a 10mm Auto carbine would be ideal. Generally field handguns for outdoorsmen like fishermen, hikers and hunters have been revolvers. But the 10mm is the one auto caliber capable of taking down larger threats. The handgun is a backup- weapon and as such used for defense.
But picture a 16.5” barreled carbine fed by Glock magazines in 10mm. It can push a 185-grain bullet through a 4.6” barrel at over 1300 fps. Given the strength of a carbine receiver +P pressures (40,000 psi) could probably push the same 185 grain bullet to near .30 Carbine velocities. The round is considered high intensity by handgun standard and factory loads go to SAAMI specs of 37,500 psi. Now consider a carbine version of the round. The 10mm Auto has a 25mm case, push that to 30mm and a SAAMI 40,000 psi and over 2000 fps muzzle velocity should be possible, great brush gun. What if?
Smaller Cartridges in Realistic Combat Ranges
The Germans realized that realistic combat ranges where under 300-400 meters and introduced the 7.9x33mm Kurz (German for short) round and introduced it primarily on the Eastern Front. After the war the Russians went to the 7.62×39 round in their SKS carbines and the AK-47. This bullet could penetrate brush and wooden stalks and trunks that absorbed the M-16’s 55 grain bullets in Vietnam. In the US, Ruger has introduced the .30 Ranch Rifle firing the 7.62×39 round which equates to about 30-30 performance. The Ruger has a .308 diameter grooves, the Eastern European guns run in groove diameters from the .308 to .312 with .311 being about the sweet spot. The M43 loading was a 123-grain bullet pushed to 2350 fps. Targeted ranges were not much beyond 400 meters or about 437 yards. 7.62×39 reloading dies generally include a .308 expander and a .311 expander, Lee and RCBS dies do. The 5.56x45mm NATO is low recoil but users are not happy with performance beyond 300 meters. With the M4’s shorter barrel bullet velocity is down and affects the penetration and energy deliverly with the 62-grain bullet. But with the extensive adoption by NATO and current difficulty in obtaining ammo in this caliber don’t expect a change in cartridges anytime soon.
Smaller Cartridges are Cheaper & Weigh Less
Why go to the smaller cartridges besides the combat range argument, quite simply the weight? The standard loadout in WWII was 80 rounds. Most carry 300 rounds and with another 300 rounds in the vehicle in the mid-eastern conflicts. Cheaper to ship, more rounds per pound, more rounds per volume, smaller is cheaper in components and lower recoil. What about a 6mm in the Russian M43 case? But if you must deal with airborne threats the bigger the better, hence the popularity of the 12.7x99mm M2 .50 caliber machinegun. We can but speculate on all sorts of ‘What ifs’.