Part of the functioning problem lies in the mag catch, and so many aftermarket 30 rd mags. Real GI 30 rounders are scarce, as so many were shipped overseas after we took the carbine out of service, and others were cut into 5/10 rounders for civilian disposal in the US. The mag catch for the M2 Carbine, designed for the 30 rounder, additionally supports the mag on a 3rd point or stud, making it lock in better. An M1 carbine can easily be swapped out to replace the M1 catch with an M2 mag catch. Some after market mags work o.k., but I would be thrifty on the price of any, and just use the ones that work with the M2 catch. There ARE counterfeit 30 round mags, so it is really hard to tell what you are getting.