HI, hope everyone is having a good November. Long story short I have a 1955 Tula SKS that was sold to me as a Vietnam "bring-back". It was without papers so I was more expecting a beat-up early import. It is well-worn with pitting under the stock and all the signs of some time in the jungle or in grandpa's damp closet. It shot well with commercial ammo, well enough to ring an 8 inch plate at 100 yards consistently. I wanted to get into CB loading for it so I slugged the bore at .312. In my preparations I decided to do a chamber casting. I was shocked at what I found. The bore measures .314, ok, a little worn, but the throat is GARBAGE. With a micrometer and a dial caliper I',m getting 0.319 just ahead of the rifling and 0.340 just past the case-neck! (see attached pic) Am I doing something wrong? How is this even possible? I was expecting a little throat erosion but .340? There is a very faint line where the case-neck ends at 0.345.
Maybe this rifle was used in combat, thousands of rounds of corrosive ammo is quick succession, or shot with corrosive surplus and put away wet.
Has anyone else seen these kind of chamber dimensions? All I've found in searching is a service offering chamber reaming to ENLARGE the throat! Will this even shoot Cast? I'd like to see some other chamber castings of SKS rifles, both worn and as-new to compare. What do you think is going on here?