I've been doing these for a few years now its totally adjustable
even if changing calibers ,there inside all the extreme rapids I've done
the P-rod ones ,where for more rearward air flow so far its been a big improvement
still messing around with then .
the crossmen barrel went from shooting Kodiaks OK
the the new barrel like heavy JSBs 18 grn jsb 16grn and Kodiaks the 18grns look like the go to pellet now for this P-rod