When I had my barrel threaded for mine the rifle went from pretty darn accurate to holes not on the paper. After much cussing I finally got on paper, keyhole. Looking back I found copper on the comp, obvious strikes. Back to the gunsmith, he said he just threaded the barrel, didn't pull the barrel and thread it concentric with the bore, so the bore was off from the exterior, which is pretty common. The only options at that point, cut the thread off and redo it or enlarge slightly the bore of the comp, which is what I did.
Even after that, for some reason the first shot after putting it on almost always keyholes, subsequent shots go fine though. It's a mystery to me, I just treat the first round as a throwaway.
If I ever put the barrel back on (it's a different caliber rifle now) with a suppressor on I'll have to redo the barrel though, too expensive to risk a strike.
