And, so you are aware, there are generally 3 main types of large frame styles or patterns. Armalite, DPMS and Rock River. Many parts are proprietary. Belonging to the owner, as in the rights to the patents filed. And because of these proprietary parts many things are not inter changeable. There is no mil spec. This isn’t an AR15.
Oh, and by the way, you are an assembler my friend, until you mechanically alter a part permanently. Then you are a builder. So untilmill out an 80%, put a barrel on a lathe, or otherwise manufacture something, you assembled a bunch of wrong parts.