The powerbelts are slightly undersized and rely on the expansion of the synthetic skirt to act as the gas check as the bullet travels down the barrel. The sabot is slightly oversized to seal off the grooves of the rifling. If you think the 1st is tough wait till ya gotta load a fast 2nd shot. Make the 1st one count! Luckily my 2 inlines love the powerbelts and shoot them well. There has been alot of discussion here about them falling apart but my test (crude as they are) show just the opposite. I will stick with em.