Bushy's use chrome lined barrels. RR doesn't. There's an Bushmaster/RR (upper/lower) rifle for sale and the pic shows the finishes don't match. I'd check to see which finish matches first. Also if you want a chome-lined barrel, you can buy a BM flattop and buy the RR tactical assault removable carry handle (I think that's what it's called) or buy the RR high rise upper and find a chome libned barrel attatched. I know, not a definitve answer, but options for you.