Gamo IGT replacement with NP2?

I have a spare NP2 gas ram and was wondering if I can replace the Gamo IGT ram with it. All the dimensions are the same except the NP2 is 1/4in longer than the IGT. I thingk the IGT is weak as it is only producing 627fps a foot away from the muzzle with a 14.3gr pellet. I already replaced the piston seal with a Vortek seal and went from 575fps to the 627fps. The breach seal is sealing I did the toilet paper test and it did not move. Will I destroy the rifle with the slightly longer NP2?