Let me relate one of my experiences with a Mosin-Nagant--a 91.30. A dealer at a Tulsa gun show had a crate of the rifles. I looked them over and could find only one in the box that had not been counter bored. (This is a process where, when the end of the barrel is worn out of round by the steel cleaning rods, the end of the barrel is drilled out a couple of inches--drilled down to good rifling.) A gun that has been counter bored has been used a good bit. The rifle that I found appeared to be new and not used. I bought it.
I took the gun to my club's range and fired it. It shot great, but the hull would not extract. I took it home and used a small oak dowell to drive the hull out. The hull had scratches and indentations on it when it emerged from the chamber. I looked, and there were machine burrs in the chamber. I suspect this problem was why the rifle had not been used very much.
I took a new 5/16-inch round file, carefully ran it into the chamber at an angle until I felt one of the burrs, then hit the burr with the file. I repeated this process until I had more-or-less removed the burrs. I then took a 1/2-inch oak dowell, cut off about 10 inches, tapered the end of the piece to more-or-less fit the chamber, chucked the piece of dowell into a drill moter, and spun it in the chamber until it wore to fit the chamber. I then put fine lapping compound on the spun-shaped dowell and polished the chamber. The rifle, after this bit of shade-tree gun smithing, works beautifully. (Lapping compound is a grease with an abrasive in it that was once used by shade-tree mechanics to grind, or seat, valves in a car motor. Comes in fine and coarse.)
Remember, this was the rifle with which the Russians fought the Germans. The 91.30's made before the war were much better machined--more carefully made. Those made during the war were turned out as fast as possible. Pretty guns were not the issue: survival was the issue. I value my war-time 91.30's FOR the visible lathe marks on the barrel. My experience with the M44's, and the M38's, suggests that they were produced with a little more care.
Incidentally, when putting a synthetic stock on a 91.30, you often have to shave out the inside of the new stock to allow that gizmo that has to do with the cartridges in the magazine to retract enough. I've forgotten what that gizmo is called. I want to say cartridge regulator, but that may not be right. I'll be 73 next week, so I don't always remember what some things, and people, are called.