I expect I'd have to pack the ram body out and it will rattle around inside the piston, Quickshot who make the ram also make a special piston which is thinner (the rams body fits inside perfectly with no slack) than the Gamo piston and has bearings and is lighter as well.
I've only tested it with the usual 'go to' AA fields as that's what it's normally the most accurate with, I've not tested the accuracy yet but it shoots pretty nice (just as good as the WW kit when fitted).
Pete