A counterbore is when the rifling and part of the inner diameter of the bore is drilled out from the muzzle back far enough to get rid of boogered up rifling.The need for counterboring is caused by poor cleaning methods, ie: not using a rod guide. counterbore is when the rifling and part of the inner diameter of the bore is drilled out from the muzzle back far enough to get rid of boogered up rifling. The need for counterboring is caused by poor cleaning methods, ie: not using a rod guide.
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