doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Birmingham Proof Pressures 1904-1925

I own an old Birmingham, Clabrough and Johnstone, sidelock double gun, 12 gauge, 2 �" chambers, proofed under the 1904-1925 rules. My question, does anyone know what pressure these old Birmingham guns were tested to. I understand that later on (1954) they were proof marked 3 � tons per square inch, does that mean 6500 psi? I am trying to figure out what is safe to shoot through it. I had been using the Winchester AA, Low Noise Low Recoil Target loads but have recently found that Winchester rates these loads at 11,500 psi? Winchester Ammunition
Thanks.
Tim

Hi Tim, the pressure will be the same, but was your gun originally chambered for 2 3/4" or have the chambers been let out? The pressures for a 2 3/4" Brit gun is 9682psi.

I would NOT shoot the Winchester AA's in this gun. The pressures are to excessive.

A pic of the bbl flats would help.

Good Luck!

Greg

Tim;
First note the British Ton used here was not our 2,000 lb "Short Ton" but 2240 lbs. Thus a direct multiplication of 3� tons would give 7280 psi. Further note this is not actual PSI but rather crusher pressure. In the modern Shotgun by Sir Gerald Burrard he gave a formula for these British pressures to convert to PSI. This formula was worked out by firing loads in a pressure barrel fitted with both lead crushers & a Piezoelectric crystal to simultaneously record the pressure of a load by both methods.
The formula was said to give a very close approximation across normal shotshell pressures as measured by the British.
The formula is; multiply the tons by 1.5, then subtract .5 ton.
Thus 3� crusher tons would convert to 4 3/8 PE tons. Multiplying by 2240 then gives 9800 PSI. Note this is in quite close agreement to the psi given above by Greg, being within 118 lbs.
I am not totally certain the Low Recoil, Low noise loads actually reach that 11,500 PSI, but Winchester simply is not going to guarantee anything other than they are within SAAMI Specs, which is 11,500 PSI for a 2 3/4" 12 gauge shell.

Tim,
Safe working pressure for a gun stamped 3 1/4 tons by a U.K. proof houses means 3 1/4 IMPERIAL Tons. This = 3.25x 2240= 7,280 P.S.I.
If the breech pressure developed by the Winchester AA,s is indeed 11500 P.S.I. they should not be used in your gun.

Thanks guys.The gun was originally chambered 2 ��, it�s not stamped on the barrel flats, but rather on top of the barrels, kind of unusual I guess. I think it is likely pre-1921 as there are no date mark stamps. I had originally thought that the Winchester AA Low Recoil loads were okay, as the Dealer/Gunsmith I bought the gun through said it would be okay to shoot low brass shells in it. Luckily no damage, the barrels still ring like a bell. It�s a nice gun, my favourite because it�s English, and pushing nearly a 100 years in age. The gun was used very little judging from the condition. Was from an estate sale, the guy said his father had bought it in the 1950's, and only shot a couple of boxes through it then put it into the closet. It obviously had another gentle life before that. I have owned it since 1991. I will try and round up some Gambore English traditional loads.
Tim

A 1 1/4 ounce proof should be a heavier proof than a standard proof. Does it have 3 1/4 tons on it anywhere? Perhaps a inquire to the proof house would tell you what it would have been proofed for. I suspect you have a gun that was proofed for a heavier load, hence more pressure.

The 2 3/4" and 3" chamberings were generally used for waterfowl or pigeon shooting, but a shooter could of course order a gun with 2 3/4" for game shooting as well. The shot charge stampings were used until they were replaced by the Tons Per Square Inch stamping under the 1954 Rules of Proof.

You have a very nice SL there. You can also used 2 1/2" RST loads available here in the States or load your own low pressure 2 3/4" loads.

Best of luck to you!

Greg

Nope, no 3 � tons per square inch marking on the gun. Thanks Greg, I never knew that about the change in shot weights through the Great War. That makes sense, then possibly my gun was built before 1914. I had previously contacted the Birmingham Proof House trying to figure out a date for the gun; they said 1904-1925 based on proof marks, and with no date mark it would in theory, be pre-1921. I had asked them about the chamber marking 2 �� on the top of the barrels and they said that wasn�t their proof mark, the Proof House would only mark on the barrel flats. I never asked about the pressure proof though. My guess is that the 2 �� was marked on the barrels at the importers request. I think the gun was likely imported into Canada by the Hudson Bay Company, although there are no retailer markings to confirm that. The gun has a very high serial #, marked 102XXX. I had contacted Larry Shelton the Clabrough gun expert, and he thought it was probably a Hudson Bay Company gun judging by such a high serial #. He said the Clabrough guns were only serial numbered into the 14000�s, but that large import retailers could ask for their own serial numbers to be put on import guns.

I don't know if I can get RST loads here in Canada. It may even be hard to get the Gambore even though Kent Cartridges distributes here. The big box sporting goods retailers don't want to be bothered with special orders anymore, they only want to sell what they specifically bring in. Whatever happened to customer service?

Thanks again.
Tim

1 1/4 Oz was the normal proof for 2 3/4" chambers.

2 1/2" chambers were usually proofed at 1 1/8 Oz.

As an aside, it looks like your gun was originally a 13/1, so would have originally accepted a 0.719 plug gauge, but not a 0.729 plug gauge.
This was quite usual at that time, but can have a nasty 'knock on' effect - in that if it now measures greater than 0.729, it would (in the UK) require reproof before sale. It is quite common to find guns originally proofed at 0.719 re-proofed at 0.729. I have one that has had that done.

John, I have a WW Greener from 1892 that has 13/1 also. Someone before when I first got it said that it was proofed at .719 but should not accept a .719 plug gage 9" into bore.
These bores measure .727, right and .728 left with .009 and .034 constriction.
From what I have gathered it is a Facile Princeps F 16 with the machine turned receiver.

So as you stated it would be good at .728?

This gun has 27 1/8" barrels and weighs 6 lbs. even. What a joy to carry, just have to get used to the side safety.
The thinnest wall thickness is .030" 17" from breech. 5 inches from breech measure .073 and .074. Barrels weigh 2 lbs. 14.8 ozs.