Will it take a standard upper receiver group?
i believe that they have a model specific bolt/buffer assembly.
other than that from what ive dug up its pretty much commercial.
edit:
even more digging, damn you Brian....
apparently the early ones (as in just after bushmaster bought the rights) had proprietary bolt/buffer, later model ones are supposed to be interchangeable internals.
i cant believe this one would be a early model one for the fact quantities are barely getting out and sitting on shelf.
the real question is, how long will it last.