This is from the GM Manual for Frigidaire and A.C. Sparkplug production during WWII. I have an original manual, and this is a fold-out from there. Yes, it's the aircraft version, but all is the same except the obvious barrel, jacket, etc. The ANM2 .50 cal bolt is the same as the HB, this before the M3 model was developed. Now, I have to credit this image to Tom Taska at KMP, as this scan was part of the package he sent out with his semi trigger bar and sear. So, hope you don't mind my sharing this, Tom. I think it will be helpful for this thread. And, I don't have a good way to scan my own original.