Is it not possible to place a dye on the BB that will transfer to the barrel when shot?
This would indicate relative speed of the BB vs. direction of travel inside the barrel and the force of impact with the barrel.
This of course assumes that the BB will actually touch the inner barel at all. But we do know from many years ago that BBs with a poor surface finish would leave streaks of their finish inside some barrels.
Age verifier Northern Alberta
Democracy is two wolves and a sheep discussing what's for dinner.
Freedom is the wolves limping away while the sheep reloads.
Never confuse freedom with democracy.