Barrel Wall Thickness ?

FRBRIT · Post by **FRBRIT** » Sun Feb 08, 2009 1:34 pm

A question came into my pea-picking head about Fox 20ga barrels. There have been numerous discussions on factory barrel weights and what they could or should weigh as per the original number stamped on them "1,2,3,4" Etc. But I haven't seen much on what do these numbers & weights mean in relation to barrel wall thickness.

Has anyone here measured many 20ga #4 weight barrels for wall thickness? These are the lightest and I assume the thinnest of the tubes that were available. My curiosity comes from wanting to know how thin they may have been from the factory and then determine if maybe some sort of work was done on them along the way, so someone might be able to know how thin is too thin?

I've always held .030 as the rule of thumb standard for wall thickness anything less than .030 to be marginal for safety concerns. Without measuring, some of the #4 barrels I've seen appear to be less than this.

Whats your observations on wall thickness? What would be the thinnest wall thickness you would trust on a Fox?

THE FOX · Post by **THE FOX** » Sun Feb 08, 2009 6:14 pm

Hello, FRBRIT
I have just measured the barrels on my AE 20, and they both are about .026 at the muzzle. They are #4 barrels. Both measure about .612 id the best that I can measure with a caliper. I have had it only for two years and have put quite a few shells through it. It is a quail shootin' dude. The barrels are 26", and I really can't tell if they've been cut or not. I'm sort of thinking about writing Mr Callahan and find out.

Bryan Clary

Silvers · Post by **Silvers** » Mon Feb 09, 2009 7:45 am

There is no way wall thickness can be measured accurately without a good wall gauge, and very few gents have access to one that will measure full length along the tube, let's say 13-16" from each end depending on the barrel length. The assumption that the bore and outside diameter (O.D.) are concentric on older SxS barrels is usually incorrect. Bore and O.D. are almost always somewhat eccentric in the completed SxS barrel set because of solder cleanup, and how striking was done. Minimum wall may be observed in the sharp corner against the top rib, joint at the bottom rib, or at 180-degrees across the horizontal axis of the barrel set.

Another factor to confuse things is the exact location where the wall is measured. The British convention seems to be to measure at 9" ahead of the breech, and 9" back from the muzzles. I suppose that is good for standardization but once you measure a few barrels on Foxes you'll find the smallest O.D. is often not at exactly 9" back from the muzzle. Anyone reporting wall thickness to you should specify where that measurement was taken on each tube. Likewise, measuring wall thickness at the muzzles isn't too helpful because the muzzle usually has more or less choke, and the O.D. at the muzzles is probably not the smallest O.D. on the barrel.

Regarding Fox barrels: I believe heavier weight graded barrels were sometimes heavily struck when lighter weight tubes were out of stock and a customer ordered a light weight gun. This can further confuse things when trying to correlate barrel weight-stamps with observed wall thickness. What is the factory wall thickness for Fox 20 gauge 4-weight tubes? Short answer, I doubt anyone has accurate data from a large enough sample set of known-to-be-original factory barrels to answer with confidence.

Is there a "generic answer" for minimum safe wall on a Fox barrel? In today's liability finger-pointing culture I doubt any competent authority would do that on 80+ year old barrels that may have been compromised by modifications and/or unknown stresses after they left the factory. JMO of course. Silvers

PeteM · Post by **PeteM** » Mon Feb 09, 2009 12:59 pm

This is a 1891 British chart of recommended minimums.

A Skeet's gauge:
http://www.brownells.com/aspx/NS/store/ ... RE%20GAUGE

bamboozler · Post by **bamboozler** » Mon Feb 09, 2009 1:21 pm

Silver's wrote:

Another factor to confuse things is the exact location where the wall is measured. The British convention seems to be to measure at 9" ahead of the breech, and 9" back from the muzzles.

Actually, the Birmingham and London Proof Houses measures the bore diameter 9" from the breech. They do so by inserting a plug gauge into the bore, the diameter of the last one that reaches 9" into the bore is the bore measurement. They measure and state the Minimum Wall Thickness anywhere in the barrel and will inform their customer if the minimum wall thickness falls below .020--even though the gun may have passed proof. One caveat, since the ribs are required to be installed prior to proof the MWT cannot be measured between the ribs. I got this information from the chief inspector, Michael Lynch, of the Birmingham Proof House.

Silvers · Post by **Silvers** » Mon Feb 09, 2009 2:13 pm

Bamboozler wrote:

Actually, the Birmingham and London Proof Houses measures the bore diameter 9" from the breech.

Greg, thanks for that info. Interesting though, when I inquiried a U.K. source a few months ago on an expatriate A H Fox gun they owned, the company voluntered the bores and wall thicknesses at 9" from the breech and 9" from the muzzle. That's not what I asked for; it's what they gave me. When I replied asking for absolute minimum wall in each tube both numbers were smaller. Frank

FRBRIT · Post by **FRBRIT** » Mon Feb 09, 2009 9:21 pm

This is all great stuff and I really hope more keeps coming in from guy's that have put the proper measuring instruments to use on Fox barrels. I really wish there was a way to get a bunch of members guns together and measure them up in an attempt at starting a data base for future reference on Fox barrel wall thickness. IMO this would be a good start at setting a base line for others to use in the future.

From the way it sounds some of the barrels that have been in use and showing no signs of problems may have pretty thin barrels.