This past summer I bought a Armalite DCM competition ar.  Along with it, I bought some junk ammo (the wolf .223) and I'm afraid I'll probably ruin my new barrel, soooooo the best thing to do would just buy a junk upper so I can just goof around and not use up alot of money on competition ammo, right?  Can I use a colt, bustmaster, etc... upper on my armalite dcm ar?

Thanks.

Any upper will drop on except a large hole Colt which would require offset pin. Try Model 1 Sales or M&A parts for a low cost medium quality upper.