Upgrading TM tac launcher spring

[Rimms]

i have a TM tac launcher which i love but its only knocking out 210fps (as stated on Z1)

basically its not packing enough of a punch and im having a bit of a problem as im finding people just aint feeling it at anything more then about 20m
i know thats partly down to them to be more aware of their hits but i want to up the fps to about 300fps and was wondering if its possible to upgrade the spring

is this possible to do, is it just a standard spring pushing the 3 pistons or is a special spring (or 3 special springs)