It will be interesting to see if your experience with the .25 cal matches mine with the .30 cal.... I found the middle pin length produced the best groups, followed closely by the deepest pin (lightest pellets)…. The accuracy with shortest pin dropped off a bit.... and with the flat base they spiralled past 40 yards or so, and by 100 were hard to keep on the paper.... A different relationship between pellet length and twist could produce completely different results, of course....One other thing I found that initially puzzled me.... was that the velocity with the middle pin and shortest pin was the same.... The shortest pin produced the heaviest HB pellet, so it should have been a bit slower, just like the middle pin was compared to the deep pin.... but that didn't happen.... I have a suspicion that the HB cavity produced by the shortest pin may be so short that the skirt is not expanding from the HPA inside it, whereas the middle and deep pin skirts are flaring outwards from the pressure and sealing tighter in the bore.... That flaring is causing a bit of extra drag, however, that is absent with the shallowest base (and of course with the flat base) pellet.... Just a theory, as I have not recovered shot pellets to observe them.... but I have no other explanation why a heavier pellet with an identical outside shape shoots the same speed....Bob