Lay the barrel on a table or bench. With one hand holding the barrel stationary, insert the hinge pin about half way into the hinge pin hole and try to wiggle it. If you can feel any movement of the pin, it is obviously not a tight fit , and obvious also is the fact that the barrel with its greater leverage advantage and the forces involved in firing can and WILL MOVE a lot more than you are able to move the hinge pin by hand. Perform this same test on the frame, but try the pin in the frame holes individually. You will also often find that the holes are not the same size from one side to the other.
Factory hinge pin hole tolerances vary tremendously.
This means that instead of just slipping in, they must be tapped in. In actuality, tapping in the pin merely burnishes down the rough surface finish inside the holes. You will also find that many of the holes are not truely round, and that only about 3 shiny spots exist where the pin has worn the blued finish off inside or polished the inside surface if the barrel or frame is stainless steel . If you can detect any movement on the factory hinge pin, then my BelIm Oversize Hinge Pin will fit. Or ask about a reamer on loan.