Hi All,
I just bought a neat 10 Gauge Hammer Gun from one of our members here and at my club. Its a Tipping & Lawdon hammer gun that is old enough to have a forend that comes off with a key rather than a latch. Its Damascus and super clean, nice engraving, nice wood with heel and toe plates and a checkered butt.
The question is the barrel flats are marked 763 with a punch BNP under a crown, a 10 in a triangle 3 1/2" 4 Tons per square inch (the square is a shape not a word and inch is ". There is also a circle with JB over an 8. The action flats have an oval with Patent No. 234 1870 above what I assume is a use or license number 1421.
I know this isn't 3 1/2 10 gauge magnum and is probably early 1870's.
I don't know how to load pics but have them....
The question is on the 3 1/2" chambers and the 4 Tons per sq in, were those normal? I have some British 2 7/8" 10's of around the same era but not marked that way?
Thanks

Reproofed after 1954. Others will know more. I can post photos for you if you'll sent them via email. PM

JB over the 8 will be the date it was reproofed . JB is the date code the 8 is the inspector .This will be 1983 .Will stand correcting on this but 4Tons will be the old Standard proof for loads such as Alpha max or Hymax . Magnum would be 4&2/2 Tons .
In 12 bore 4 tons would be Standard 3" or 2&3/4 magnum equivalent .

Burrard reported in 1955 that the "Highest Mean Service Pressure" of 4 Tons was 12,320 psi = 850 BAR
The standard 10g 2 7/8” load was 1 7/16 oz. 4 Dr. Eq. at a standard service of 9,296 psi and max. service 11,984 psi
He didn't report the 3 1/2" standard

I was under the impression that 2 7/8" was the standard 19th century ten bore chamber length but I also see older nitro proofed British guns with 3.5" chambers (I have one). Was that also a standard chambering or have these been opened up and re-proofed subsequently? What was the standard load for 3.5?

Argo, pictures sent and thank you.
This is very interesting so far, I assumed the gun had been nicely restored as it is probably the oldest non-muzzle loader I own and in fantastic shape. It never occurred to me that it had been through a modern re-proof as well.
I plan to shoot it mostly with 12 gauge light target loads in 10/12 gauge mate silver sleeves, but it sounds fine for my Sherman Bell 2 7/8" bismuth loads too, in fact they are way lighter than its current proofs.

We use low pressure loads not for the barrel and action concerns but more for the stock. Every gun passed proof but no guns stock was subject to proof. Wood dries with age and gets weaker due to stress. You crack a stock due to heavy recoiling loads it might be the end of the line for your gun. So we go for 1 ounce, 1100 fps 12 loads because that’s what it was meant to shoot. We find pressures in the 5-6,000 psi to keep stress on the barrels low. I shoot barrels as thin or slightly thinner than .020 without worry. It’s all about location and shell selection.

A few of the images of the 10 bore. Really nice:

I seem to remember seeing a Damascus hammer Purdey at a show with reproofs of 4 tons and 3 1/2" chambers. I assume they were reproofs, don't remember the shot load specified. However, my Damascus Greener eight has 3 3/4" chambers and 2 1/2 ounce shot load specified, which appear to be the original proofs. These are just WAGs, however.

Somehow, I would not be rash enough to shoot 3.5" ( 1 7/8 - 2 1/4 oz ) loads in a vintage bar action gun ( originally proofed at 11G ). Re-chambered and Re-proofed at magnum 10G ...Another glaring example of the unknowing pandering to the....unknowing?
ps - what weight is the gun ?

I love buying damascus hammerguns in 10 gauge. They settle into the hands well drop birds and clays with ease. Shooting 12 and 16 gauge inserts is a real hoot. I love going to the skeet range and when I get to station 4 I will slip in a 5 dram black powder load. Lots of noise from the gun and from your fellow shooters. If you have a heart condition, this is not advised!