doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Muzzleloader marks as to gauge??

Has anyone seen muzzleloaders marked as to gauge? I have seen a couple that are marked "13" on the underside of the breach near the forend. The "13" appears next to the provisional and final proof marks in one case involving Birmingham tubes. Because of the size of the barrels, I have guessed that the "13" may mean that it is a 13 gauge muzzleloader. Is that right? If not, what does the 13 refer to?

Here you go Rich
Gauge was marked starting with the 1855 Rules of Proof
Bore dimensions and marks post-1887 Rules of Proof



If a plug gauge of 0.710" diameter (but not one of 0.719") will enter the bore to a depth of 9" the barrels would have been marked 13.

BTW: Bore in inches was marked starting in 1954; in metric starting in 1984 to the 1889 Revisions.

Note that most of the muzzle loaders were built prior to 1887, so they do not have the tween sizes, only whole number sizes. My I Hollis M/L double with Birmingham proofs is marked 12. On M/l'ers I believe the normal practise was to gauge it at the muzzle.
My I Hollis has the mark which indicates it did not undergo provisional proof, only final/definitive proof but with the provisional charge. I forget the date this was introduced but would make it a quite late for a M/l'er.

Thank you both. That is very helpful.

Several of my 12 ga ML and Early cartridge guns are marked 13, which is about .720 I believe. It was primarily done to insure that the 12 ga fiber wads were a TIGHT fit.

Like most things British, it's confusing to us Colonials
13 lead balls .710" in diameter = 1 pound
BUT 13 gauge barrels were often bored .720" for ball

Bore and ball diameters Act of 1868
https://sizes.com/sports/shotguns.htm

Per the 1868 proof act the diameters given are the actual weight of a ball of which that many would weigh one pound. The actual marking by the proof house was done with a series of plug gages. The 13/1 etc "Tween" sizes were not used prior to 1887, thus a bore marked 13 could be anywhere from just accepting a .710" plug to just not accepting a .729" one (12 gauge). The Gunmaker himself could bore it to any size which he deemed desirable, the proof house just marked it as to what gage plug it accepted. I don't really see much confusion there.

Thanks for all the interesting comments. My barrels are .702 and .706, which I think is on the cusp of 13 gauge and 14 gauge, based on the table that Drew provided. My working hypothesis is that I have a muzzleloader conversion, on which the converting gunmaker chambered the converted gun for 12 gauge shells.

I have 4 English percussion doubles. All are marked on the flats by gauge (10, 12, 14, 15). Not all are in proof however, after more than a century of service, honing and boring.

Here is a picture of the proof and other marks on the underside of the barrel:



I believe that the barrels, used in a muzzleloader conversion to an underlever breach loader, were 13 gauge rechambered to 12 gauge for the conversion. I measure the bores at .702 and .707, on the cusp of 13 and 14 gauge according to Drew's chart. I note that there is one provisional Birmingham proof mark and two final black powder proof marks. Does this mean that it was tested twice?

Many thanks for everyone's input.