It can help with rifles, especially if they are using spherical propellants. I tried shooting 2520 in my M1A one year and discovered I could reduce the group size from about 1.2 moa to about 0.7 moa by deburring the vents. However, it never made any difference to stick powders in that gun. The reasonable stocl choices could most all be tuned to 0.7 moa in that gun without the extra step, and weren't improved further by it. Only the harder to ignite powder was. In a rifle that was capable of benchrest groups, where a smaller improvement could be detected, it might have been different.
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