That's pretty darn good accuracy but be warned those Remongton pins are "in there" and when you drive that pin out be ready to grab stuff!
Brownells sells a jig which makes disassembly easier.
Your gunsmith possibly installed a stronger spring. Ask him.
I doubt if the "vibration" has anything to do about accuracy, but it could.
Check your bedding and if not glass bedded you might try that at the recoil lug. It sounds like something else causing your problem - do you handload - tayloring your load might help.