Ok, thank's for the replies. Reason I was asking was because i wanted to use a real AR lower for a gas airsoft rifle I have. The rifle uses a self contained "trigger pack", similar to an HK rifle, that drops into the lower. So the whole FCG cavity in the lower has to be machined out larger. Since i live in NYC where getting a real functioning AR lower is next to impossible, I figured I could have a smith in another state purchase the lower, mill it out and then send it to me.
But since that won't fly then I guess I will have to take an 80% and do it myself. Just to be clear it will not function as a firearm once I'm done with it.