I keep reading that since BM bought out Professional Ordnance, they have made some changes to the Carbon 15 (specifically Type 97) rifle.  I have a PO Carbon 15, type 97 rifle, and am wondering specifically what changes were made to the rifle by BM.

Heres what i think of both  [puke]

Aren't the BM lowers 100% compatible with all AR parts vs the PO lowers that were not?

I have both PO T97 rifle and handgun. I've never had a single problem with either. It appears that PO made the rear pin lugs on the uppers thicker, and will not allow it to mate up with a conventinal lower(will contact area near buffer tube). You could easily grind/file off the extra material for a good fit. Bushmaster has (from what I understand) done this already, so the BM is compatible with any lower.Plus added a strong ejector spring.

Bushmaster has covered this in their forum in the Industry section.  In a nutshell they use less 'custom' parts and more 'standard' parts.  A good example is the new ones use standard AR-15 bolts.

According to them you will be ableo to switch uppers back & forth - but for the Carbon lower you will need to use a different (and shorter) bolt carrier in the upper.

With my wife having a new Bushy 97S, I can say Forest is 100% correct.
The lower could be altered to take a standard buffer tube and stock, thus allowing use of a standard bolt carrier, buffer, etc. Something we might be experimenting with in the near future.