12 or 11 bore?

[Eterry]

I recently bought a 12 bore double. The seller stated he'd had the barrels ultrasound for integrity. The muzzles mic at .750" and are 30".
Is it a 12 or 11 bore? She carries Belgium proofs, but not much else is visible.
Very nice wood, but the forend has a few splinters I believe can be easily repaired. The nipples are bad, beat down from decades of dry firing. I had them soaking in ATF. The locks are strong as per the period, both hammers have some slack and need shimmimg.
I bought this for my niece, but she's in love with my William Moore. I may have to break her heart.
Pics to follow..

 

[tenngun]

.75 is just about eleven gage and a bit
Howsomever if you shot a ball in it you would likely shoot a 12 (.725) in the gun

 

[Rock Home Isle]

The Brown Bess is a .750 calibre, 11 gauge…

 

[Eterry]

 

[Eterry]

I know it isn't a Bespoke gun, but I think it's a ways from what W.W. Greener called a Sham Damn gun.

 

[SDSmlf]

The muzzles mic at .750" and are 30".
Is it a 12 or 11 bore?

Call if whatever you want, but a .750” bore is pretty much nominal for 11 gauge. I forget the exact bore diameters on my Pedersoli 12 gauge double (they are slightly choked), but I know I use 13 gauge wads and cards when using purchased components (Mike’s Quality Black Powder Shotgun Wads if I recall correctly, a great place to deal with).

Basically, don’t worry about the ‘gauge’, just measure and size components accordingly.