doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Chamber Wall Thickness - Brit Guns

Hi all, what is the normal wall thickness ahead of the chambers on a Brit double?

What is the minimum?

Thanks as always!!

Greg

That's like asking how much does a car weigh. London Best game guns tend to have thin walls by American standards - maybe 28 thou or so.

I've never measured a Birmingham boxlock NE barrel but I bet they're thicker.

Minimum is what passes proof. 20 thou is considered thin; I have been told that 18thou barrels have passed proof. Dunno for sure. I think there used to be a legal minimum but again dunno for sure.

Greg,
I am most comfortable with "about" .1" in the area immediately in front of forcing cone. That said I have had light guns with much less and they seemed OK.
Bob Jurewicz

UK Working Standards recomended minimum wall thickness measured 18" from the barrel breech from Double Gun Classics p. 56, Vol. 1, No. 4 Jan-Feb, 2006:
2 1/2" 12g - .028
2 3/4" 12g - .032
Re-proof recomended minimum - .024

The Hunter's Encyclopedia
From the German proof house: minimal wall thickness at the end of chamber, regardless of length, for 12, 16 & 20 gauge guns should be 2.3mm (.0906") for 'Ordinary Good Steel' or 2.1mm (.0827") if a 'Special Steel' was used.
For the 24 & 28 gauges, due to their higher pressures, 2.4mm (.0945") was recommended.
Minimal wall of .6mm (.0236") was recomended in the "forward third" of the barrel.

Christopher Austyn Modern Sporting Guns
"There is no legal minimum thickness for a shotgun barrel, although the British Gun Trade Association recommends 20 thousandths of an inch as a general minimum."

The area just in front of the chamber will be much thicker than .020. The often mentioned .020 min. thickness would be more in the middle or the muzzle end of the barrels where pressure is much reduced and the need for metal thickness is much less important.

On American guns, the are just in front of the chamber has not decreased much below .080 or .100 of the chamber area. I was given a old Belgian single shot that has less than .050 metal over the chambers and .040 on inch in front of the chamber. Thank God no idiot reamed the chambers to 3". It would have come out the side if they did. It is scary thin when you look at it and by the looks it has digested many a shell. I refuse to shoot it and keep it just to show others. No one has offered to shoot it yet.

Not directly related but a site that I find very interesting is

www.dave-cushman.net/shot/shotshellloads.html

Tons of very good information about chamber measurments and bores that has saved me from buy more than one reamed out set of barrels.

Hi all, the reason why I asked is I measured the wall thickness on my Brit guns (which are all in proof BTW)just in front of the chamber/forcing cone area (toward the muzzles) and getting readings of between .80 and .90. None of the chambers have been let out.

To my understanding .90 is the minimum.

I have shot these guns for a couple years with low pressure 2 1/2" loads with no problems.

So...........safe or not?

I have a feeling that if most owners of Brit guns were to measure theirs they would be surprised, in or out of proof.

Your thoughts?

Thanks again and all the best!

Greg

Whoops! I gave barrel thickness - sorry.

Greg, I don't know what the "minimum" is but I agree many of our guns are much thinner than we'd like to think. Or, perhaps we'd rather not think about it at all--out of sight, out of mind. And it's sure not limited to English guns. I shoot a couple of Parkers and Lefevers with original bores and outside that appear to be stout in all respects. However, when the truth gauge (wall thickness) is run in it gets scary. Both of the damascus Parkers I'm thinking of are about .090 in front of the chambers and the Lefevers are around .025 a foot in front of the breech. But, you know, they've handled about every type of ammunition over the past 100 years and continue banging away today (with low pressure loads). So, I say go ahead and enjoy your guns but don't feed them Wally World bullets.

Greg: By your description, all of your guns are unaltered and in proof, and your new wall thickness gauge is coming up with measurements that are reasonable, and perhaps even typical, assuming 85 to 90 thousands is a safe minimum standard, as has been suggested. The "area ahead of the chambers" is of course imprecise and open to interpretation, and the segment between the end of the chamber, forcing cone and "regular" barrel wall, given its abrupt transitions and complex angles, is no doubt difficult to measure. That said, as long as the guns are unmessed with, and you're shooting the kind of ammunition intended for them, with loads and pressures approved by the proof house, I don't think you need to worry.

If you remain concerned, you'll probably get both more, and more specific, advice by sharing details about your guns, such as their age, make, type of steel, interior dimensions, specific proof marks, etc. TT