M2's are a blast. Like mentioned before, there are usgi and there are later commercial copies. Most if not all of the copies are investment casting for receiver material. National and federal ordnance, Plainfield, universal, Iver Johnson to name a few. I'd say Plainfield would be the better of the commercial bunch, but I'd much rather have a usgi receiver. A usgi receiver rarely wears out, so don't rule out a registered receiver. Barrels can be changed with ease, and parts are everywhere. As someone already said, Inland and Winchester were the only two usgi manufacturers of M2 carbines, made at the end of ww2, early to mid 1945 dates. Post war, they converted regular m1 carbines to m2. There is no receiver modifications needed. So, you'll see registered underwood, rockola, saginaw, postal meter, and so on. Early models of winchester, rockola, some fluke inlands, and all quality hardware carbines use a removable spring tube for the recoil spring, so it's not recommend to use them as a host. They will work, I've done it, but the books say not to. I've got every book and carbine tool if you need any help.