Clocking Of Components

So, how accurately must the blocks be clocked? Pretty darned close! All blocks are set at 90-degrees +/- 30-minutes, 0-seconds measured from block centerline to the top rail of the receiver. What does this equate to? Consider that the centerline of the barrel is parallel to the centerline of the gas chamber. The distance between these parallel centerlines is 25,0mm. Expressed in a lineal unit, the value of 0-degrees 30-minutes 0-seconds is about 0,2mm (0.008″) so the centerline of the gas chamber can be within +/- 0,2mm (0.008″) of barrel centerline. The rear sight block and front sight block have the same tolerance applied.