MIKE GEORGE says: I would begin by looking at all of the external screw heads on the gun. There should be no chips or burrs in or around the screwdriver slots, or scratches on the heads or on the surrounding metal.
Gunsmiths are most fussy on this point, and always use screwdrivers which fit the screw heads exactly.
The screwdriver slots should also all be aligned in the same direction, in a fore-and-aft plane in line with the axis of the barrels. That’s another point on which good gunsmiths are very fussy.
Got a question? Contact: firstname.lastname@example.org or Sporting Gun, PO Box 157, Stamford, Lincolnshire PE9 9FU