Would make no difference to the rear piston as the two pistons are locked together by the rack and gear mechanism and move at the same speed as each other. The .22 pellet obviously will travel at a lower f.p.s. but the ft.lb. energy would probably go up as bigger bores produce more efficient use of the compressed air. You can illustrate this by trying to suck a thick Mcdonalds milkshake through a thin straw, a real struggle. Fat straw very easy.
Baz
BE AN INDEPENDENT THINKER, DON'T FOLLOW THE CROWD