I have a hammerless antique English 12 bore with a chamber that is too tight to fit a standard 12 gauge shell, but too large for a 16 gauge shell.

I thought perhaps 14 gauge but the bores measure .735/.735.

Any thoughts? Brass shells only maybe?

Maybe a candidate for chamber sleeving down to 16ga?...Geo

Proof marks or a chamber cast would be a good place to start.

Could it be for a thin brass case? .735 is a 12 bore or maybe a 12/1 bore. What do the chambers measure? A 12 should be .812 tapering to .800 give or take a few thousand. 14 is .775 and .763 with bores .693.

Show us a photo of the proofmarks on the barrel flats.

Most" brass cases fit the same chamber as do paper cases. There were a few made with undersize chambers for smaller cases but they are extremely rare.
At least these were cataloged in the US, can't say for certain if any were made in England or not.

Bore size isnt all that relevant; do a chamber cast and put a picture up of the proof marks and get someone to measure it properly with a shotgun bore micrometer or plug gauge 9" from the breech

Is there a visible end to the chambers or can you see a forcing cone? Chamber-less guns were experimented with usually designed for use with brass cases.

Bore size is almost irrelevant, ive seen 12 bores which were 11 in the bore, and 12 bores that were 16 in the bore. You could just as well have a 14 bore

The diameter at the breech should be around .812 for a 12 bore and about .775 for a 14 bore. Make allowances for wear and manufacturing error and such.

How about trying a 14 gauge shell in the chamber, a lot cheaper than taking a chamber cast.

I guess the length of the shell wouldn’t matter? As if the gun has short chambers.

The gun is marked 14B over 15M.

So clearly this is a 14 gauge that has been over-bored. Which I guess wasn't that uncommon.

Thanks for the replies.

Is it an early gun? I had an 1879 Greener hammer gun that had started life as a 12, but had been hogged out to a .783 (10 gauge) bore with 2 7/8 chambers. Despite that, it still had .110 at the forcing cone and .22/.23 MWT in the distal third of the barrels. Left the shop with a lot of meat to spare apparently.

Yes the proof marks place it in the 1875-1887 range.

Jason, you may want to read through this - very similar situation, as I described above, as to bore measurements wildly off the proof marks. I really think it is something about that era of guns, but don't have anything more than anecdotal suspicions:

http://www.doublegunshop.com/forums/ubbt...7087#Post417087

This is a bit of a red herring, you are quoting the 1875-87 proof marks commonly accompanied by 'NOT FOR BALL'. However this is the proof size (the 14B; the 15M is the muzzle size giving the choke constriction) NOT the chamber size. Sadly at this time, there was no chamber marks (in a diamond) so the only way to tell what the chambering is to measure it or use some kind of Go/NoGo gauge eg catridges of the various different gauges. Note that there were some very odd sizes promoted by some gunmakers like 14 1/2 bore by Lancaster I think. There may have been others. At this time there was very little standardisation and ANY chamber size could be encountered albeit rarely.
Enjoy!

Thanks Toby. I will measure the chambers.

Maker?

Also, remember that prior to 1887 the between bore sizes were not marked, bores were marked by whole gauge sizes only. Thus a bore marked 14 could have started life at anywhere from just accepting a 0.693 " plug gage to just not accepting a 13 @ 0.710".

I have a Birmingham proofed W Richards with bores marked 14 which has 12 gauge chambers Bores while heavily pitted now measure very close to that 0.710" diameter.

Have the bores been enlarged or the chambers re-cut, frankly I don't know. It was my Grandfathers & he was not a hunter. It was simply a utility gun. I have no idea at what time he bought in but my Father remembers him having it when he was a youth & he was born in 1910. I seriously doubt any modifications were made to it after my Granddad acquired it so is most likely as it left the factory. It is a side lever hammer gun with the lever on the left side. I wish it were in shootable condition, but unfortunately, it saw years of neglect before it came into my hands.

My choice of inexpensive "go-no go" gauge for this project is a store bought 14 gauge shell. Whomever provides you with a modern 14 gauge shell should be able to tell you where to buy them, that is, if it fits.

Any pics of this gun?

You will have an easier time finding rocking horse dung.