It seems that those short-barreled rifles burn propellants inefficiently. People call this a "pistol cartridge" when it is obviously generates higher pressures than the .357 S&W Magnum (38,500 psi as opposed to 35,000 psi). The only handgun cartridge that exceeds the .30 Carbine is the 9 X 25 Winchester, and there's not much call for that cartridge in a "light rifle" is there?

So let's quit fooling ourselves by calling the .30 Carbine a pistol cartridge when it's genesis was from the .32 Winchester Self Loading Rifle Cartridge. The .30 Carbine always has been a rifle cartridge and will never be sufficiently efficient in shorter barrels. It is hard enough to gain performance from the Ruger's revolver barrel. (I shot a friend's Ruger in .30 Carbine and it was extremely loud and not efficient at all).

While it worked inside the tunnels for "short range shock effect" it wasn't much above ground.

Its time to face reality.