The two 10 gauges I have, one top lever made with 50,000 SN range, and an underlifter made with 25,000 SN range, have identical .793 bores. Like many of the early 12 gauge guns that have bores around .750, many of the early 10 gauge guns have bores in the .790-.800 range. I think it was Austin Hogan (if I'm wrong on that credit I apologize, for some reason I remember him discussing this topic) that plotted out a 12 gauge chart showing when the big change that took place in tooling for 12 gauge boring, and after that change 12 gauge guns were bored to the modern .729 constantly. I would guess 10 gauge guns followed that same path, but more research would be needed. I think it was concluded that measuring the chambers was the only reliable way of determining the true "gauge" of the gun.