If your using a scope on your combo gun it should work. If your using the factory fixed sight you might have a problem with changing point of impact. You are working on an irreplaceable barrel any mistake can be VERY expensive. Do you think that you will gain enough to make the project worthwhile. The little 222 Rem is a dandy cartridge I use mine on coyote out to 300 yards. If you think you need more, I'd really look into a different combo gun. There are plenty out there in 5.6x50R Mag(mine is a Bernardelli) and 22 Sav Highpower/5.6x52R(mine is a BRNO 305).