I bought a new Mossberg .410 SA over the weekend. I can't get any of my shells to chamber in it. I used a plug gauge to measure the chamber and the largest I can get to fit is .474.
I did a chamber cast and it read at .4751 a few hours after the cast. I think it was around .4746 shortly after the cast.
My reading of the chamber specs says that the chamber should be .4811 -0/+.005
Am I reading the blueprint correctly? Is this chamber too small?