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

Where it is thin is the real major point. Out near the muzzle is much less troubling than near where I stand and hold the gun. I know of one gun that passed proof with .017 barrels not long ago. That was near the muzzle not near the chamber end. When you see just "passed proof", do not assume that that means the barrels are robust, just that they did not fail when proofed. Like I mentioned earlier thin barrels are very easy to dent. If you are looking for a shooter I would be very leery of any gun with barrels thinner than .025. If you are looking a collector type gun, which will be rarely if ever shot, then thin should not be that big of a deal. Just handle them gentle.

Looking at a psi chart I copied off of a Doublegunshop topic, the highest pressure load that was tested had about 9800 psi one inch from the standing breech; the lowest 8700. These, I believe were three nitro and one black. At nine inches all loads were under 3900 psi.
Interesting the the lowest chamber load retained the highest psi down the barrel; probably a slower powder.

I have the original.





Please note the bold print at the top of the graph. Too many times in the past incorrect assumptions were reached regarding these tests. They developed these loads to all have the same muzzle energy. They state that the Dupont Oval load is special. In the bottom image, they included a 5th load, progress nitro. It produced a lower peak than black powder.

10" out from the breech and they are all above 3000. It seems to me that is pretty close to my hand....

Pete

I have seen a gun come back from successful proof with 07 thou minimum!

Generally, a barrel with 17 or 18 thou is fine as long as it well up the tube. Just don't dent it and don't pay too much for it!

A friend of mine has a Purdey SLE with damascus barrels down to 17 thou. It is lovely and he only paid �5000 for it. I told him not to dent it. He has been shooting it happily for five or six years.

Unfortunately, he is too mean (cheap) to buy a decent gunslip and dented it last time he went out by banging it inside the gun bus.

The same gun with 25 thou in the barels would have cost him �10,000.

Take your pick.

PeteM;
I believe if you look closely at the 2 charts you will see that powders B, C, D & E of the original with 5 powders listed became A, B, C & D in the newer chart. When the 2nd chart was published the powder A (Ballistite or equiv) had been discontinued & was dropped. The testing was done by DuPont de Nemours & Co, with the 2nd chart showing only 4 of the powders from the test being published by The American Rifleman in the 1950's.
You will note that powder A on the chart did exceed 10K pressure, but this was a 3 DE load pushing 1�oz of shot, not a pip-squeak load by any means. I believe that Hercules Red Dot powder is very closely related to the old Ballistite. I have some 50+ year old data giving loads for Red Dot with 1�oz of shot. With todays components it is pushing it to keep pressures in line with 1 1/8oz loads & it seems to be most useful for 1oz or under loads.
It doesn't take a very thick wall to contain 3K pressure, but I would not want it to be very thin at that point either, better safe than sorry.
Once you get out beyond about 15" then bbl wall thickness is more for rigidity, dent prevention & general integrity of the bbls, than for containing pressure.

In the smaller gauges, are the minimum barrel wall thickness rules of thumb the same ?

In other words are the higher pressures of smaller gauges offset by "Hoop Strength" ?

Doc - who did the "considering" and who did the "changing"?

Per Christopher Austyn, the former gun guru at Christie's when they still auctioned guns, in his book "Modern Sporting Guns": "There is no legal minimum thickness for a shotgun barrel, although the British Gun Trade Association RECOMMEND 20 thousandths of an inch as a general minimum." (Emphasis the author's.)

Postoak, I've never seen different thicknesses recommended for smaller bore guns.

Larry that is interesting, given the (generally) higher pressures of the Small Gauges.

Just happened to be looking through a bunch of old articles I've saved. Here's a quote concerning pressure from Les Greevy's column, Shooting Sportsman, Jan/Feb 01: "According to Dick Quesenberry, product engineer for Alliant Powder, modern intermediate and slow-burning powders generate their peak pressures from 8 to 12 inches up the barrel--not far from where you hold your leading hand."

I don't know anything about Oval or MX, but I know that black and bulk smokeless both supposedly generated their peak pressures very quickly, as do modern fast-burning smokeless powders. But I was surprised to see someone (who should be in a position to know) suggesting that slower-burning powders take that much longer to reach peak pressure.

Going back and looking at Bell's "Finding Out For Myself, Part VI: Smokeless vs Black", it would appear that the above graphs actually date back to a test run by DuPont in 1933. But from Bell's article, his test results also indicated--as shown in the graphs above--that all the powders he tried (FFFG, 7625, Universal Clays, Blue Dot, and Clays) produced their peak pressures quite close to the breech. All, in fact, within the first inch or a bit more. Makes me wonder about the 8-12" quote from the Alliant engineer.