Rusty & old

Hi all. Going to throw this question out see if anyone has an answer. Just brought a Weihrauch suppressor (second hand) put it on my rifle made it a dame sight quiter. Then thought I'd go shoot a few rabbits missing them by miles to the left. Scope still zeroed not moved put on my old one pellet on pellet opened the Weihrauch and found 2 washers with nicks in them. Drilled and dressed them put back in still going left. Anyone have any ideas? Cheers all