12ga barrels question

[Roberto S Siciliano]

I have an opportunity to buy a PB 12ga hammer gun circa 1888. The owner says the bore at the muzzle end of the barrels is large like a 10ga muzzle. He's not shotgun friendly and I'm trying to figure out if the barrels have been re-bored along the way or if there was such a PB gun made that was bigger at the muzzle.
I might be able to pick up the gun at a good price but if the barrels have been tampered with, I'm not interested.

Any thoughts about this are appreciated.

[Dean Romig]

Without a bore mic and a wall thickness gauge you’d only be guessing and buying it might prove more costly than “a good price.”





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[mobirdhunter]

I don’t know where you are, or if the seller would agree, but if there was a more experienced member near you that could help you evaluate the gun, that might be a good option.

[Roberto S Siciliano]

So here's what I found out.
The wall thickness at the muzzle is 1.32mm [0.0519685"].
The left barrel gauges at full choke. The right barrel is in the 10ga range. Could this be factory... or was the right barrel re-bored. Is 0.0519685" muzzle thickness acceptable?
Photos are attached.
Comments appreciated.

Originally Posted by Dean Romig

Without a bore mic and a wall thickness gauge you’d only be guessing and buying it might prove more costly than “a good price.”





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[B. Dudley]

It is not too uncommon. I recently had a 12g C grade hammer gun in my shop with 10g boring. Built that way.

[Roberto S Siciliano]

lft.jpg

Rt.jpg

gauge.jpg

[Roberto S Siciliano]

Is a wall thickness of 0.0519685 [1.32mm] at the muzzle acceptable for firing, assuming there is no serious pitting?

Originally Posted by Brian Dudley

It is not too uncommon. I recently had a 12g C grade hammer gun in my shop with 10g boring. Built that way.

[mobirdhunter]

Drop in gauges can be very deceiving in regard to wall thickness at strategic points along the length of the barrels. The only good way to ascertain the wall thickness is with a gauge that can be put into the barrels far enough to measure their entire length from both muzzle and breech.

[Milton C Starr]

I have seen quite a few Parker 12 gauges for sale with bore diameters in the .750" range and 10 gauge Parkers with bore over .800" so you cant go by bore diameter exactly . Seems like on old American doubles they usually run a bit bigger on bore sizes and on English guns they run a bit narrow . It should be noted SAAMI specifications didnt start until 1926.

[Roberto S Siciliano]

Thank you gentleman. Your contributions are exponentially contributing to my learning curve.
Much appreciated.