doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Calling Crossed Chisels- min wall thickness???

Perhaps Erik Koik(aka Rufus Scout and others) would like to chime in and say a few words his thinning .020 James Woodward after reading this?

A little simple math sez the following. Hoop stress (for thin walled cylinders) is estimated by pressure times cylinder radius divided by wall thickness. The pressure is on the order of 1500 psi at the mid-point of the barrel. Radius will be something near 0.365". Thickness is stated as 0.015". And, the answer is 36,500 psi stress on the barrel wall. Soft steel yield stress is typically in the 50,000 psi range. The stated thickness of 0.010" gives a hoop stress of 54,750 psi.

As you can see, this is getting into the range where it doesn't take much more going wrong to get at least a bulge; yielding the barrel wall under pressure will make a bulge.

How about those experiments by Greener who bored the barrels down in increments looking for the thinnest of thin that may still hold? I don't know the details and don't have the original source so I might have misunderstood the whole thing.
I also want to err on safe side and would prefer a thicker barrel.
Looking back at previous messages on this site it seems that the minimal recommended barrel thickness at the far end corner of the chamber should be a minimum of .09" and barrel thickness at its thinnest at least .02".
Please correct me if I'm wrong.

Greener worked on the muzzle end only - far as I know. Pressure there would be down to, oh, say less than 500 psi. A 0.005" (foil) at 500 psi would have the same hoop stress as the cited 0.015" at 1500 psi. Greener is reputed to have removed the "foil" choke with a pen knife - I can believe he did, too.

Note that a 0.090" wall at the tippy end of the chamber could easily see 10,000 psi. Say the chamber was cut to 0.780". Then, we have a hoop stress of 43,333 psi. Hmmmmmm!!! Maybe you would want to keep those chamber pressures down if you are shooting a gun with a thin chamber wall??? Hoop stress for a 0.125" chamber wall would be 31,200 psi for the 0.780" chamber and 10,000 psi chamber pressure. The 0.090" wall would have 32,500 psi hoop stress with 7,500 psi chamber pressure.

Rocketman,

Thank you for your info.

Gentlemen of the Web,,,,,I am surprised after reading all these letters' that nobody has mentioned the "Oft Quoted" Boss made the lightest barrels in the London Trade'(More often than not'by a dealer who had found that someone '1 step ahead of his page in "How to make a Quick Quid(Buck)"had managed to( Theres no way to be delicate here)Stuck the gun into the aperture of his person, where the "Sun seldom shines")I have examined Boss and Woodward Barrels with the "Super-Lightweight,Thin-Walled Barrels"(One set .013 min wall thickness)All one has to do is measure the "Bores @ Proof" ( As pointed out by previous, Well Informed "Weber Warriors" .729 = 12bore) Boss never bored a set of tubes proofed at .729 & 50 yrs later they measure .742 @ 9" from the same breech, and they had not been through 'Re-Proof"!! The Dealers Sales-Tag said 'Special Original" Boss Lightweight Barrels" the Min Walls were Thirteen Thou'! I think the Riveling was thrown in for free....And the 'Deal was" the price was reduced down to $27.500.00! I suggested that the"Gent who had listened to the rhetoric from the"Business-Suited,Ivy-Leagued" Salesman get a 2nd Opinion from "Another Member of the Dirty-Hands Bench-workers Brigade..Alfred Gallifent....I dont think the Boss with"Big-Bores &Very Thin Walls" has shown up on the East-Coast again! I'm sure I've upset someone who is trying to peddleGuns with the "Grand Old British Gunmakers Names"(And Lock-Plates .014"proud of the "Oft-Sanded "Head of the Stock".....(Photos on File) but thats what we get paid for!!May Bill Johnson Rest in Peace! See Dallas "Boss Best guns Only"(Bill J' stocker in the Golden Years...CC/dt

In the realm of "famous British lightweight 12s" please consider the thought that a thin barrel made to be that way may have more merit than a barrel that came to be that thin-walled...

I still like at least 20 thous in even guns touted as light weight from around 1900.

Is there any data to show that original lightweight barrels were made of higher strength steel? If yes, then the thinner walls might be OK. Otherwise, there would be no difference, with the possible exception of bore diameter, between barrels honed thin and barrels bored and struck thin by the original maker.

Running down to the ragged edge of strength seems foolish if you think about putting the thing up in front of your face with your hand wrapped around it...never mind you have to start considering fatigue failures when you get close to yield strength.