doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Minimum Wall Thickness Revisited

Not to my knowledge. At least nothing that has ever been published. Ultimately the gun designer has to know what material will be used in the barrel. Once that is known everything else follows.

Now about the DuPont chart...



I have been through this booklet several times. I am 100% sure that they state they used lead crushers to obtain their data.

To the best of my knowledge, piezo was not in common use then. It would have been easy to create a probe that could be correlated to lead, copper or whatever you choose. The equipment, ie oscilliscope, they used was primitive by today's standard. Limited to about 10mhz, single trace, no memory, etc...

There was a serious discussion in the literature circa 1915 about the lead crusher standard of the day. It was fully recognized that lead crusher was a flawed method. Mainly because it had a built-in inertia which prevented the capture of smaller values. This shows in the chart, they stop at 10" from the breech. Not because they considered the data irrelevant, but because they knew the lead crusher system would not give them accurate information below about 3,000 psi.

As Larry B has pointed out in the past. They had so much data based on the lead crusher method, they could not bring themselves to simply walk away from it.

For my own use, I will not knowingly fire a gun that has had the chambers tampered with. I measure my guns to be sure of wall thickness. I do not trust a dealer nor those in their employee with my fingers.

If I want to shoot the heaviest loads, I have a Baikal for that. Built like a tank!

Pete

AM is right. It's not bulging or bursts that are the real problem, it's how much life is left in the bbls.

Thin walls cannot be repaired, so a dent or a bulge in the wrong spot will put the bbls out commission.

If thin walls were a problem and minimum thicknesses needed to be established, the London & Birmingham proof houses would done it and they would fail any gun with walls below the minimum.

In the past they did not do this, and as far as I know they still don't.

OWD

An article from the American Rifleman dated Sept 1931 shows a bunch of pressure barrels, all utilizing the crusher method, then in use by the major American arms and ammo makers. I don't know how accurate readings were farther down the barrel, but the article makes the following statement:

"These barrels are fitted with five or more additional pistons at intervals from the breech to the muzzle." The purpose was "for a better understanding of the rate of burning or characteristics of pressure curves." Pretty much the same method Bell and Armbrust used, except theirs employed electronic transducers, in Bell's "Finding Out For Myself" articles.

As for failing guns with thin walls, Vic Venters' current article on proof in Shooting Sportsman indicates the proofhouse does not do that, although the British "trade" still recommends MBWT of .020.

Read Bell if you want to know where the pressure is.

Burrard gave much insight into this pressure bit. In fact he laid out a chart showing, using normal bbl construction & a normal load of the powder in then current use, just how far from the breech it would even be possible to burst a bbl, barring a metal flaw or an obstruction. A flaw can of course allow a bbl to open at less than normal pressures, though generally not with the violence of an obstruction. An obstruction due to the sudden checking of the charge moving down the bbl creates a very high localized pressure spot.

Beyond this a normal bbl, once the charge has moved a ways down the bbl, could actually hold the closed cell pressure if it could be just brought up to this level. This situation does not normally occur though as if the bbl is plugged the ugly affect of the obstruction rears its head & if the powder is spread down the bore it is extremely difficult to get ignition.

Botttom line though is that as long as the metal is sound & there is no obstruction in the bore, it is virtually impossible to burst a bbl very much ahead of the chamber. Technically though, all things considered, the juncture of the chamber with the forcing cone is the weakest point in a shotgun bbl. Fortunately though max pressure has already begun to subside when this point is reached, so it is normally of no consequence.

Sums it up really .
Makes you wonder however why everyone is so precious about minimum wall thickness.
In reality the only issue I can see with thin barrels is the likelihood of damaging them.
As long as the chambers have not been lengthened and the chamber/forcing cone area is free from pitting what does it really matter if the bores have been honed out of proof?
We seldom talk of minimum chamber/end thickness,but would not that be more logical from a safety viewpoint?
Makes you wonder why guns are deemed out of proof with only 5 tho or so wall thickness removed.


GDU

Taken from Griffin & Howe

16. Barrel Wall Thickness - The thickness of the walls of a shotgun barrel. It is reasonable to assume that guns built by responsible manufacturers are safe to shoot, when new, with the loads for which they were intended. As the decades go by, however, as barrels are or buffed for rebluing and as occasional pits are honed out of the bores, steel is gradually removed from the barrels. The barrel walls, already built thin for lightness, become thinner still. At some point they become too thin for safety. It is important to know the barrel wall thickness of an old, well-used shotgun before shooting it. A rule of thumb states that the minimum barrel wall thickness should be .020" in a 12 gauge gun.

They should sell what they state. Wasn't it not so long ago a gentleman here bought a gun from them, had some work done and found out the barrels wall thickness was below above #16.

Yes, I believe so. I was just showing another example of what the opinion of "acceptable tolerance" is. Whether someone follows the accepted norm is another matter.

It has nothing to do with you and what you posted. I just saw the name in the heading. If that particular event did not happen, I would be ok with them. There are more stories out there of what we think are reputable dealers and find out they are not.

Sorry to put this on this thread as it is a very important subject.