redneck whitesox PBR,
The markings on the uppers are what the forging manufacturers use as a date stamp. After they run however many thousands the letters will change. The finish, dry film lube on the inside of the upper, V-shape stamping on the carrier key & barrel markings will tell you, you have a genuine Bushmaster upper.
That is not correct, the only manufacturer that stamps there own upper forging is Colt. They stamp a C on all of theirs.