Does anybody know if the barrels on new 20" Bushmaster A2 guns are button rifled, machined, or formed by forged around a mandrel stuck in a hollow bore?
Straight from Bushmaster...
Bushmaster Barrels... are the finest AR15/M16 type barrels made - machined from Chrome-Moly Vanadium steel - Rockwell C26 to 33 hardened. And we now offer 20"/24" Heavy Barrels in Stainless Steel! Most Bushmaster barrels are hard chrome lined (except the Stainless Steel barrels) to offer corrosion resistance in the bore and chamber. Chrome is more than twice as hard as barrel steel and effectively doubles barrel life with proper care (exactly why the military specifies the process). Chrome’s lubricity (i.e. “slipperiness”) reduces friction, increases velocity, aids in chambering, extraction, and speeds barrel cleaning. Bushmaster barrels are manganese phosphate finished (again except the Stainless) to guard against exterior rust or corrosion, and to provide the matte black, non reflective finish found on quality military arms.
Rifling… Bushmaster barrels are button rifled with 6 grooves and lands (right hand twist, 1 turn in 9", except for DCM barrels - 1 in 8"). Our experience is that the 1 in 9" twist offers the best results with the widest variety of ammunition. Most barrels are heavy profile their full length - to help alleviate barrel whip and inaccuracy in rapid or full-auto fire.