possible with any gun.
Fact is if you change cal it will either make pellet faster or slower depending which way you do it.
I'm sure that if you go from 177 set up to 22 it will make the 22 fly faster and break the law and if you go from 22 to 177 it will go slower.
Either that way or the opposite.
.177 flys faster and flater then a 22 ,most air guns can been changed ie .22 500fps@11.5ftlbs / .177 770fps@11.5ftlb
theoben use a gamo trigger unit in the mk1 ,up um till 2006 then there changed it to a mk4 trigger same as mk2 rapid/mfr
may mk1 has the gamo ,and if there are set up right i think there are just as good as the mk4 trigger
atb with your sale Mark
what if i take a 300cc tank in will they still need an adaptor? im new to precharged mate
take it in to them thee will have fitting for it somewhere am sure