the early univerals were made from "left over " surplus military parts after they ran out . universal had jobbers make the various parts needed to complete the guns. beside universal there was iver johnson and plainfield and now auto ordinance.the companies that made carbines for the military are standard products,inland/gm,winchester,irwin-pederson/saginaw, underwood,national postal meter ,quality hardware, rock-ola. i might have missed one or two. ? be forwarned a complete m1 all original are harder to find. when sent to the armorys after the war they were all stripped down and when put back together very little thought went back into matching parts. since they were all interchangable it's now common to find a winchester receiver with a quality hardware bolt on a rock-ols stock etc....it was mix and match , john is almost correct the 30 carbine rounds though developed for the carbine is more akin to a pistol round than a rifle round. however no one made a 30 cal pistol until ruger in the early 70's ? and amy made a 30 cal auto in that caliber for a short period of time . i think ?
even though surplus ammo has dried up , it's a great gun to shoot lots of fun and damn handy as long as you use good mags and stay away from the after market junk. oh and as for the 30 round mags most on the market are crap. the good ones are m2 mags made for the auto version of the m1