To keep this fairly short, I took a fired high brass shell and drove the primer out with a punch. Then I inserted a long bolt through the inside of the primer pocket and secured it tightly with a nut on the base. A � bolt was snug enough that I had to �thread� it through the primer pocket. I chucked this in a hand drill. This gave me a mandrel with which to apply some JB Bore paste and I slowly lapped the chamber. I kept doing this until a spent round chambered in the barrel with the same resistance as the other 12 gauge. Once I reached this point I finished the polishing with some Simichrome metal polish (probably could use tooth paste).
I hate to bring up an old post, but I am having the same issues with my new 870 Super Mag. Could you go into a little greater detail on how to make the "buffer" out of the spent casing? And, are you just taking the barrel off the gun and securing it in a vise the working the open end?
