[Rick Lee]

Yes, it's just about all compatible after the upper and lower receivers, which are sometimes caliber-specific, and the barrels are, obviously, always caliber-specific. A few years ago I bought a Spike's stripped lower receiver, a RRA lower parts kit and then all the other parts that I wanted on the lower. Then I bought a complete upper from Del-Ton, some Magpul handguards and it all fit together like a Swiss watch. Shoots as well as my out of the box Bushmaster ever did.