The standard bore size for 10 ga is .775. Many of my early Parker hammerguns in 10ga often seem to have circa .790 bores. As for choke, the sizes are very much like 12 ga with .040 being considered full choke. If the bores of your gun are .800 at the muzzles, I suspect you have no choke...depending on frame size if your gun indeed has .800" bores, I'd check barrel wall thickness. Many of these old guns were bored a number of times and they are often seen with larger bores in the first 12"-18" in front of the breech while having slightly smaller bores to the muzzles do to amateur barrel work to remove pits (often just prior to sale
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