doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Wall thickness opinion

Dustin: could you please explain the pressure spike 9" from the muzzle?

Turn-of-the-century powder pressure-distance curves



c. 1930 powders and loads



Modern powders



I believe gun sellers report MWT at 9" from the muzzle because that is typically where the barrels are thinnest ie. about 20" from the breech and before the start of choke constriction. And IMHO that is not an adequate assessment.

just to be clear, I believe the pressure peak is 9" from breech, not muzzle

9” from the breech is where the proof house measures peak pressure in France.

.022 wall thickness gets my attention, not in a good way, in any older gun, especially if it was not proofed at that dimension. The .022 reading is out there, at 20” from the breech, the pressure is dropping at that point. I wouldn’t attempt to use the promotional loads on sale at Wally World, but, with decent low pressure stuff, it sounds like it would be fine.

Show us some pictures, Milt.

Best,
Ted

Builder: I do not read where you have said whether the gun barrels are currently "in Proof" or not---are they?

Stephen Howell

Stephen, I am not sure if I fully understand the Belgian proofmarks nor did I spend much time yet on researching. There are a lot of marks to deal with on the flats and on the barrels. Some, I have no idea what they are. My initial concern was simply measure wall thickness for safety and go from there. I just got the gun two days ago in the evening. My guess is all the barrel work was done in the USA.

I will take pictures as soon as I can and post them here. I think members might find it interesting.

Drew,
I don't know if you said what you said as a "gotcha" moment or not, but where did I say in my post that there is a pressure spike 9" from the muzzles? Where did I mention pressures at all?? I know you fancy yourself as a barrel specialist or "hobbyist" and you do manage to post oodles of tasty info here on the subject (a lot of which I have looked at, reviewed, discussed and learned from over the years), but have you actually done any type of barrel work? Do you know how barrels are struck down and shaped to accentuate the beautiful lines that most of love about a SxS shotgun? If you do, then you already have an idea that as the barrels are struck down to the proper profile, they are inherently getting thinner as we get to the muzzles.

The 9" from the muzzle being a crucial area for measurement is because when SxS barrels are struck down, prior to finishing, the sharpest taper and thinnest area where there is still significant pressure in the barrel meet up is usually going to be in that very spot. When you get down to the .020 MWT in that area, that is getting extremely close to not being a reliable amount of steel left to ensure that that area is going to hold together. It’s not definitive, it's an estimation. Now let’s talk about repairs; if that area of the barrels is now .020 after a dent or crease has been removed, that .020 area of steel might be somewhat fatigued. Think of a piece of plastic that is continuously bent, it starts to form that fatigue line in the material and we all know that it’s weaker and about to break. While metal isn't plastic, metal behaves in much of the same way. Figure in Damascus steel, high or low quality doesn't matter, and now your dealing with areas that have been welded that might already be somewhat weaker just due to the way it was constructed. I shoot damascus guns too, I've read all of the Bell articles, I'm not saying damascus is a death trap, but I wouldn't be shooting one with a MWT below .025. That's just me.

We've all seen old hammer guns with muzzles that are razor thin. I suppose one could say "I shoot a gun with .010 wall thickness and I've never had a problem". It really does depend on the location, how many times has the metal been fatigued prior to that thin area getting to its current MWT, what type of material is the barrel made from, what type of ammunition is going to be used, and lastly, what are you intending to do with the gun.....Hunt it? Strictly use it at the range? Safe queen?
If you're going to hunt the gun, you have to think about damage that might possibly occur while your doing that...if you happen to dent the barrels and the damage occurs at an area of .020 MWT, that's going to be a problem. If you're occasionally shooting the gun at some clay targets using appropriate ammo, then you might be ok... until your not.
When it comes to resale, more discerning buyers will simply pass...aka, your gun with .020 MWT becomes very difficult to sell.

If the gun has passed proof with thin walls, all that's saying is it didn't give way during that test, but who knows what would've happened if they fired another proof pill (?).

I simply asked a question Dustin. I've never claimed to work on barrels, in any manner. Research does however provide information, with which we can make decisions.
And this is what you said
".022 is awfully thin if that spot is where the pressure spike is going to be (usually around 9” from the muzzle)."

Do you understand my confusion?

I have no idea why but I find when I see muzzle and breech I have to think a bit to remember which is which. When quickly typing, it is real easy to use the wrong word--at least for me. Front and back would be a lot easier. The bullet comes out the front of the gun. Enough said.

Ya I do. I misspoke. Sorry about that. Did the rest of my post make sense?

Great discussion - interesting and useful.