If your bore might be ruff or have burrs you might push a cotten ball through with a jag if any of the cotten hangs up then thats where the problem is, usually unless it is very bad burrs or a rough bore will cut rather than shred an patch of course 777 does tend to shred them, but when it happens with a load like 65 grs I would start by checking the fit of the ball and patch, there should be plan easy to see marks where the patch material was pressed into the pure lead ball by the bore and light ones where the riflings are. if thats the case then check you bore like Cayquad said its likly you have some problem in one of those areas.