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.
Nooooo!!! Don't use a completed lower receiver to build the airsoft gun. Use it to build a full AR-rifle where it is legal to do so
For the airsoft, just get one of these 80% receivers that are available at various build shops and work on it a bit. The airsoft gun doesnt have to be perfect. The real rifle must be!
You live in NYC though so be really careful about your laws. AR parts, especially lowers, even unfinished ones, are like peanut butter to an allergic person.