doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Damascus barrel wall thickness

"IF" you were to cap off both ends of a shotgun bbl & pressurize the entire bore to the bursting point, obviously it would burst at the weakest point. This would almost certainly be the point where the wall was thinnest.

However when you fire a shotshell in said bbl a totally different circumstance exists. The pressure reaches its maximum inside the chamber & falls off rapidly as the shot moves down the bore, increasing the combustion area.

In relation to the pressure curve the weakest point in most shotgun bbls is the juncture of the chamber & forcing cone. As the charge nears the muzzle, then of course the entire bore will have a fairly uniform pressure but far less than it was in the chamber & it has been shown on several occasions even bbls of extremely thin walls will withstand this pressure.

It must also be borne in mind & obstruction does not uniformally pressurize the entire bore behind it, but instead creates a localized area at the obstruction having a high pressure. In the case of an obstruction the bbl will burst at or very near to the obstruction itself, irregardlesss of the bbls thinnest point. Many bbls which I have measured have the thinnest point back somewhat from the muzzles with the wall thickened as the chokes are approached. If an obstruction is lodged there at the beginning of the chokes the bbl will still either bulge or burst there, rather than at the thinner point behind it. This really has no bearing on firing a normal load through an un-obstructed bbl.

It is noted that when Bell blew up two Parker bbls, one steel & one damascus, they both finally gave way as pressures were around the 30K psi range. "BOTH" burst in the "Chambers", not down in the thinner sections of the bbls.

All of this has been well documented from way before I was born & I'm 73 years old, I didn't "Discover" any of this.

Jim, I may have been the person you are quoting. About 2 years ago I was requested by the owner of a family gun to have it nitro re-proofed as he wanted to export it to his son in the USA and it is illegal to export a shotgun from the UK if out of proof.
The barrel walls had patches that measured 0.014" and 0.015" respectively about 18" from the breech.
It sailed through 2 1/2" nitro proof and as you may be aware there is no pressure difference between standard 2 1/2" and standard 2 3/4" proof, it is just a matter of chamber length.

P.S. The gun had Damascus barrels.

I do already have what I believed to be the answer, and that was that it would not be an issue as long as it was forward of the forcing cones... that seems to have been the consensus here also. It is sometimes nice to get the consensus of many others to ensure you are not far off base. It is also a way to learn... if I never asked a single question about old shotguns from the ppl that know a great deal more than me, I would not learn about them and thus it would follow from your logic, I would not own any.

And I will say, there are not many of THIS gun available.

2 Piper and others, thank you, I did read the Bell article and I think of it often when I hear ppl yell and scream about how unsafe old damascus guns are to shoot. I do own my own BWT and a bore gauge and feel comfortable checking out my own guns prior to shooting them I was just looking for opinions from others on what they considered safe.

Thanks, I will post pictures in a few days whether I end up with the gun or not as I think its worth discussing.

Toby,
Most of what I hear on the subject comes through Eric Woods. He was partnered up with Alan Crewe for a short while in London, then came over here to work with Trevallion. Probably the best, relatively unknown, gunsmith around. The man works magic with a piece of steel and a file.
Jim

Most are just bought to ogle over anyway....if yer just a ogler I say go for it.

As Jim pointed out, what we have to remember here is that our current 1 1/8 oz loads aren't the equivalent of the 1 1/8 oz load which was designated as the working load for your gun. Back when that gun passed proof, all British 1 1/8 oz loads were within certain pressure parameters. For American 12ga loads, current max pressure would be 11,500 psi, which is likely 20-30% higher than those old loads. Not to mention the fact that today you can buy 1 1/8 oz lead loads with velocities up around 14-1500 fps, so recoil will likewise increase dramatically. Neither of those things are good for old guns.

I've owned several British 12's proofed for 1 1/8 oz loads. For targets, I shot mostly 7/8 oz reloads in them, occasionally 1 oz, both loaded to very low pressures. I did use some 1 1/8 oz reloads on pheasants, but they developed just a little over 7,000 psi pressure.

Not too correct Larry but as further reinforcement - SAAMI standards are Max Average pressure in a lot of ammo should be 11,500psi. However, there are two additional pressure limits the gun must be prepared to withstand. The Max Probable Lot Mean would be 12,100psi and the Max probable Sample Mean is 13,000psi. This tells me my 12ga firing factory ammo could very well be subjected to 13,000psi periodically. Whereas 12ga damascus barrel was originally built around an 8000psi load or less. The British reproof pressures are actually very similar to SAAMI but because they are measured with slightly different placement of the transducers appear different.

Joe,

I don't buy guns to "ogle" over...

To all else, I would only shoot 2.5" light loads through this guns so it should not be an issue. Thanks again and some interesting facts.

i know a fox owner who has an original low weight fox with BWTs around .018-.019 and he shoots 3" shells through it... just another one of those stories...

Actually, unless things have changed recently, those pressures are not measured with transducers at all. They're still using the lead crusher system. Or so the Birmingham Proof House said back in 2001. They gave standard CIP proof and service pressures, converted to transducer psi, as 13,920 and 10,730.