I know that somehow this works well in in this semi-auto rifle, but not others.
Though I don't have an M1 carbine, I do cast for a Saiga in 7.62x39 and for .357 mag., so perhaps some thoughts may transfer...
1. The #1 issue (as I understand it) casting for rifles is velocity. Rifle velocities and pressures are very high and present a greater challenge wrt. leading, gas cutting, etc. And though you won't find many handguns chambered for .30 carbine, it is, none the less, essentially a pistol cartridge, very much comparable to .357 mag. (which many, many people cast for).
2. The concern with gas operated semi-automatics seems to center around clogging up the gas port as vaporized lead precipitates out on the surfaces of the gas cylinder and piping. I'm not an expert, but it makes sense to me that gas systems that move a lot of gas through generously sized ports and loose fitting pistons will be much less affected by any lead coating. With the Kalashnikov based actions, the gas piston fits loosely into the ribbed cylinder and both are easy to access for thorough cleaning.
3. Gas checks, though they add cost, do prevent a lot of the problems associated with pushing lead boolits fast. You don't typically see them used, however, unless your pushing well over 2,000 fps. Where typical M1 carbine loads (as I understand it) are in the high teens.
I want an M1 carbine so bad I can taste it.... All opportunities to get them at reasonable prices seem to be long gone though.
