I've got one of those early Irwin- Pedersen M-1 carbines that was assembled by GM at Grand Rapids from the existing IP parts. I believe they encountered some heat treating problems that would not let their initial test guns pass the sustain fire testing. I know the Army rejected all of their entire first order and that's when GM offered to take over the Grand Rapids plant. They were already heavily engaged in M-1 carbine manufacture in Saginaw, MI at the time. They quickly rectified the problem, used all the existing IP parts up first, and continued on. Legitimate IP carbines still carry a high premium price.