It's easy, just remove the bolt kit, unscrew the back cap from the top hat and slide one or two rings onto the top hat until they're snug against the ridge at the front where the top hat threads into the beer can. It's not recommended as such but I remove the outer o-rings to make installation easier (they don't have to seal anything), and DO NOT put any lube on the outside of the top hat as you don't want the rings moving about once fitted. Then replace the bolt kit, air up and chrono, adjusting the HPR to bring velocity to where you want it. If you notice any dropoff try one ring instead of two but I fitted two to my brother's PM6 at the weekend and he reported a significant increase in shots with no other issues, the gun wasn't noticeably louder and didn't break any paint.