With all this fuss about the BM59 receivers, guns, blah blah blah for sale, it is important to answer some of the questions I've had about what is Hoyle in a BM59 receiver. "Hoyle" means by the book to those that don't play poker.
Here are some photo's of what a BM59 receiver mod should look like if it is supposed to look like a "Real" BM59. We can only take this mod so far though, we cannot put the left side receiver cut out in for the selector and we probably cannot put the right side receiver cut out in. Without further a-due, here are photo's of a BM59 mod from my shop.
Finally, I do not anneal and then reharden my receivers. I spend the money on Carbide end mills and leave the USGI hardness as it was in all the vital areas. If this is important to you, check with your builder to see how they do it. If it is not important, no worries.
By the way, if someone wants a receiver that just takes a BM59 magazine but has nothing else in common with what a BM59 receiver should look like, it's much less expensive to do.
I felt everyone should know what the differences are in what will "work" and what actually works AND looks right.