Designed with service rifle and high power competition in mind, Criterion-manufactured Heavy Service Rifle and NRA Match contour barrels offer extreme accuracy potential for competition shooters. Uniformity of the bore, groove, twist, and a hand lapped finish improve the accuracy potential of each match quality barrel. The 1-7.7 twist on the 20" Heavy Service Rifle model allows for improved performance with heavier 80 gr. Sierra MatchKings without sacrificing the performance of lighter ammunition. These barrels are offered in both pre-ban (1/2x28 threaded muzzle) and post-ban (11deg target crown) configurations. Note: Chambers are finished, but barrels should be headspaced and installed by a qualified gunsmith.