Bushmaster barrels are marked B MP (twist rate)

Colt hasn't marked anything regarding chrome on their barrels in at least 25 years.  That was originally done in the mid/late 60s, to indicate that replacement barrels were chrome-lined, as the original mid-60s barrels were not chromed.  By the mid 70s, Colt and all military manufacturers had gone to a standard format:

C MP 5.56 NATO 1/7

C = Colt or whoever the manufacturer is.

M = Magnetic Particle Inspected
P = Proof Load Tested

5.56 NATO = Chamber Dimensions (this is the marking for the military chamber dimensions)

1/7 = Barrel Twist Rate


A Bushmaster barrel, let's say a 16" HBAR 1:9, will be marked:

B MP 5.56 NATO 1/9 HBAR

Note that the "HBAR" isn't any kind of military requirement; Colt put that on their civilian barrels in the 80s when the HBAR was first released, and marking them that way is kind of a tradition now.

A Bushmaster DCM barrel will be marked:

B MP .223 REM 1/8

These are match barrels that use the SAAMI-spec .223 match chamber, and they have a 1:8 twist rate.


-Troy