Barrel Groups, slug liners, and Fx Impact MK1

Good afternoon gentleman, I’ve got a a slug liner and barrel group on it’s way, with my gun being a MK1, I’m shooting the 25 grain jsbs at 950fps. Once I switch to .22 pellet probe at I going to lose my power? 

Ive got a 700mm barrel and slug liner coming, will I have the ability to reach that 930fps threshold to fire the slugs accurately? 

Thanks.