MSP Ret,
The rifling starts right at the front end of the breech plug, so you would have no problem. I have the 24" bbl, and I have been using 90g of TS ffg. Might try TS fffg to squeak out a little more velocity in the shorter bbl. With steel rings and scope, the whole thing weighs 6.4 lbs. The 3 50g pellets are roughly equivalent to 120g of TS ffg, or probably 110g or less of TS fffg. Even the 24" bbl is still approved in the manual for 3 50g pellets.