Just a thought and I could be wrong but is it the speed of an unbalanced BH or the spin rate of the shaft that causes it to fly wrong? When I was young and did a bit of machining you could true up a piece of unbalanced steel at low RPM, if you went to a higher RPM it would try and throw the lathe apart. With my sons arrow we make them ourselves and I reduced the angle of the 2inch blazers till I found that point where the arrows fly best.He has no trouble grouping out to 40m and I get him to aim at different dots on the target because he cuts flights off. His specs are about 60lbs, 470g two blade at about 292fps.