When not deployed as a National Guard soldier I am part of a small type 07/02 manufacturer. We got started just to do R&D for suppressors for fun but we have also built a number of post sample MGs for fun (and as test fixtures for suppressors). Based on what I've read here and other places I've decided to do a post sample RPD just for the fun of it but my question is what piece would I register as the MG? Since I intend to use an unmodified semi auto receiver it would have to be the internals and I suspect the bolt carrier would be the right piece because it activates the fireing pin and fires the round. I know some people here are also manufacurers so this has to have come up in the past. Just wondering.