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

Several variables involved: wall thickness itself along the barrel, pressure along the barrel (CIP or SAAMI?), critical points along barrel related to shooter anatomy, risk avertion of shooter, other considerations such as propensity to dents.

Hey guys,

I have measured dozens of factory original, non altered American doubles that had a spot behind the chokes that got down to .018. Parker 20ga. guns on "O" frames that were ordered light weight had to ditch metal somewhere. These were original blue, original bore diameter guns in high condition. The Shooting Sportsman magazine Sept/Oct 2009 issue had an article regarding concentricity of Holland and Holland barrels and in the first 3 paragraphs addresses that question very clearly; industry standard is .020 3-10" behind the muzzle if I remember clearly. I have a copy scanned to my files if anyone wants to read it. email me at shachterj@aol.com

fxe is correct. Many guns, both American and English, have skinny barrels from the factory. That doesn't make it right. It also doesn't make me want to buy one with those barrels. I own a ten gauge Sauer bird gun that weighs 6 pounds 4 ounces and its wall thickness is closer to 30 than it is to 20. I have no idea how they did it, but they did it. The Brits shave their barrels down, inside and out, and send them to the proof houses and they pass proof. That doesn't mean I would buy those butchered up guns. If I get a chance, I will measure a few 0 frame 20 and 28 gauge Parkers and see whether I agree with fxe. By the way, Joe is right. Looking at .020 on a micrometer or vernier caliper will scare you.

For those who don't always have a vernier caliper handy... I used to set the points gap on my '69 Chevy truck to .016" with a paper mathcbook cover as a feeler guage. This needed to be done about once a month because the distributor shaft was rough.

So lay a blonde hair on a paper matchbook cover and you are looking at about .020" That's not a lot of material between 8000-12000 psi of hot powder gasses and your fingers and eyes. I spent about a half hour totally blind from a head seperation on a rifle cartridge, so excuse me for being a bit gun shy when it comes to thin barrels. That was a very long half hour.

two tenths, twenty hundredths, two hundred thousandths, whatever it takes! For the decimally-challenged, conversion to fractional inch can help with visualization.

.25=1/4"
.125"=1/8"
.062=1/16" approximately

Those who have been primarily involved with yeas and breadbaskets as size standards have trouble with all systems.

jack

Quick translation: Joe, Keith, and I don't buy any .020 shotguns.

Another thing that occurs to me is the difficulty of measureing shotgun bores, what if you are off a couple of thou ?

That .020 could be .018 or less ?

Would that be a natural or bleached blonde ?

"IF" you have .020" wall over the "Chamber" which is where that 8-12Kpsi occurs you are "In a Heap of Trouble Boy.

W W Greener reported on making a bbl so thin, "In the forward Section" that after it had "Held" for a number of shots with normal shells, he ripped it open with his pen knife. As long as no obstruction is present there is little danger of "Blowing" the forward half of a bbl.

Incidently. though I have not personally done a lot of checking I was always told a "True" Blonde's hair would mic too about .003", A Brunette's .0035" & a Red Head's @ 004".
Though not quite as much fun an easier solution is to simply lay a strip of 20# printer paper on the matchbook cover.

Notes on Proof and Barrel Wall Thickness of Shotguns

Here at George Gibbs Ltd we have a policy of selling secondhand shotguns with a minimum of .004" of proof size remaining and a minimum of .025" of barrel wall thickness at 9" from the muzzle (for shotguns of 28 bore to 12 bore inc)

We will sell guns with measurements of less than these figures but will indicate the sizes and offer the gun at a reduced price. The reason for this is we hope that any gun we sell will give years of service for the new owner and with our minimum measurements,we feel we can repair even quite severe damage to barrels eg dents , pitting , without compromising the owners investment in the gun.

Our experience tells us that shotgun barrels with a minimum wall thickness below .025" ( 25 thousands of an inch) are not dangerous to shoot nor are they more likley to fail a proof or reproof test , however the thinner the barrel the easier it is to dent them and the harder it is to repair them , indeed the repair of thin barrels makes the barrels even thinner thereby compounding the problem ! This is why we adopt our policy on wall thickness , in order as practical gunmakers to give you , our customers , good service and peace of mind .

This is what I find out here www.gibbsgunmakers.com