Hatsan What is the best pellet for Hatsan Striker 1000s 1.77

Gamo pellets are over priced garbage and slugs are about pointless in a break barrel. Look into some 8-11gr pellets from brands like JSB , H&N, JTS, QYS, Norma, RWS, or even Crosman and Benjamin.

There is no way around it. You're going to have to do some testing to see what your barrel likes. The JSBs and H&Ns even come in various head sizes for testing purposes and they even have pellet test assortments.