lancaster good tip. Thanks.

daryl,

Not clear to me what that information will do to limit my options? Brass can be turned to any OD. So; eventually I may need that. Plastic will expand to fill any chamber size. I dont have a spec for old Winchester brass or paper.

My best measurement is the chamber has no taper and measures somewhere around 0.935 to 0.938

I found CIP spec for modern plastic 8ga (not the industrial USA loads). Nothing on any brass old or new.

CIP modern ammo has a chamber that starts with a diameter forward of the rim of 0.931 min to 0.935 max and it tapers down from that.