Bob308, Chances are it's a Keystone, they did make replacement C's with the correct A4 bolt relief. The thing about Keystone, most of the time upside down "K" in the cutoff notch are almost impossible to make out. They were a little more bulky than the Springfield C's, it's hard to explain how to tell without getting them side by side. When you grip them it's a world of difference. Yours would have been replaced with a replacement stock by some individual. If it had been done at an arsenal there would be markings.