My Parker 12 is actually an 11-gauge?

[Lloyd McKissick]

I was down at the shop last week to measure my most recent acquisition (mainly to confirm wall thicknesses in these old "twist" tubes) and to show it off just a bit to the owner (he's more of a British gun guy but he was actually quite interested, especially in the "fishtail" top lever as he'd never seen one before).

Everything was as expected until we measured the internal bore sizes of the gun. I've probably heard (or read about) this elsewhere (even here maybe?), but this 1887 Grade O hammer has a significant overbore for a 12-gauge gun, like 20k plus. The chambers are in spec for a 12 bore but the tubes are approaching 10-gauge in diameter. Even with that overbore, it still has lots of constriction (choke) left in both tubes. At 23k, this gun has been honed a fair bit (& the choke on the left tube is slightly less than what's in the right), but it's still fine (it has a minimum of 23 thousands width at it's thinnest point, about a foot from the muzzle) and all this "overbore" does (other than helping keep pressures down) is make it possibly pattern a little better.

Since I'm basically lazy (sigh!), instead of digging through the webpage archives I'd like to confirm my observations with the "cognoscenti" here. Is this a common discovery amongst the earlier Parker guns?