.308x.300×12 twist,4 groove,hammer forged barrel blanks with integral 308 Win.chambers,chrome-moly 22 1/2″”long x 1.135 O.D. test runs at Fellows Gear Shaper Co. Springfield, V.T. in the 60s for M14s. Bores have a mirror shine and chambers are about 1/4″” extra deep for fitting. Will finish at 21 1/2″”. Those tested shoot very well.