Can you put any length upper on a receiver? Have a RRA  and would like to have a 20" to swap out my 16" from time to time.

Quoted: Can you put any barrel length upper receiver on an existing lower receiver?

With the exception of older "large" pivot pin Colts, the answer to the question above is YES.

Mike

well, not any length...


Can't a large hole upper be used with an adaptor?

Look into the P.O.F. I own one, its a real nice upper. Its the new piston set up. Clean,and runs great. It has fixed the down falls of the gas system of the standard AR. And now that they have got the bugs worked out of the first few. They seem to be the winning set up. Just a little costly. But you get what you pay for.

Just my opion. Check out some thread's on here.

But you already own a great lower. Basic construction, start with a good base..