Terry, that Jeffery would be classed as chamberless 12 bore although I agree it is more of a 10. I have some ammo in my collection for one of these. The headstamps are marked 10/12. Some of these were later re-chambered to accept the 3 1/2" 10 bore cartridge and re-proofed accordingly as the thin brass ammunition became obsolete. Lagopus.....