Proof House
 

I think part of the key here is that the Proof House Proof Tests. So they do not merely pass the gun because it has 20 thou, they shoot it with a proof load and see if there is enough THOU to avoid POW. :eek:

And, it does seem like I have seen more pressure problems with small gauge guns than with larger bores. Don't remember enough physics to recall if a cylinder of a larger diameter would be stronger than a cylinder of a smaller diameter for a given pressure.

OK, so the measurement was made by the seller. That is not the way this game is played. The way the game is played, rule #1, is "You buy a Manson wall thickness gauge from Brownell's for about a hundred bucks, measure the wall thickness yourself." Only then do you buy any old gun for more than about $300.00. If my measurement showed .024, I wouldn't be interested in the gun.

Barrel Thickness
 

I believe the .025 number comes from a hoop stress calculation by Oscar Gaddy.

Best, Austin

Add to the FAQs?

UK Working Standards recomended minimum wall thickness measured 18" from the barrel breech from Double Gun Classics p. 56, Vol. 1, No. 4 Jan-Feb, 2006:
2 1/2" 12g - .028
2 3/4" 12g - .032
Re-proof recomended minimum - .024

The Hunter's Encyclopedia
From the German proof house: minimal wall thickness at the end of chamber, regardless of length, for 12, 16 & 20 gauge guns should be 2.3mm (.0906") for 'Ordinary Good Steel' or 2.1mm (.0827") if a 'Special Steel' was used.
For the 24 & 28 gauges, due to their higher pressures, 2.4mm (.0945") was recommended.
Minimal wall of .6mm (.0236") was recomended in the "forward third" of the barrel.

Christopher Austyn Modern Sporting Guns
"There is no legal minimum thickness for a shotgun barrel, although the British Gun Trade Association recommends 20 thousandths of an inch as a general minimum."

Nominal Parker Barrel Thickness
 

We measured the outside diameters of several Parker barrels to attempt to generalize barrel taper. These tables will appear in the Spring Issue of Parker Pages.
Parker barrels are hand filed, and the outside of the barrel is not concentric with the bore. One cannot simply subtract bore diameter from outside diameter to determine thickness. However, examining several barrels and subtracting the nominal bore diameter allows one to estimate the nominal thickness the filers were trying to produce.
Analysis of 22 twelve gauge barrel sets, including three sets weighing less than three pounds, indicates the nominal minimum barrel thickness at 24 inches is 1/32 inch. Eccentricity may cause portions of the barrel to be thinner than this. Minimum nominal thickness at 18 inches would be about .050 inches.
If those of you that have barrel thickness gauges would like to make up tables of actual measurements, we will publish them in a later issue.

Best, Austin

Bill,

I had planned on that (already have a gauge) but knowing .024 is borderline, I was only seeking second, third, fourth, etc. opinions before I wasted the time to get the gun in hand. That's the opinion I was looking for, that if it was .024 you'd pass on it every time.

Thanks.

That's sure not my opinion. Once again, it's a matter of where the .024 is. If it's in the last third or even the front half of the barrel I wouldn't worry about it at all if the rest of the barrel is solid. I think a whole lot of Parker guns would be tossed aside from "thin walls" if the owners really knew how thin they are. But many of them were originally struck quite thin and they've gone a hundred years with nary a problem. Why not another hundred. Find out where the thinnest portion is and then make your decision.

I was told by a gunsmith who deals with a lot of refurbished English guns that the London proof house limit was .018". Anyone ever seen that number used?

I have one with .730 bores and is in the .023-.024 range if not very close to original... maybe barrels where re blacked..... maybe bores where polished it's a 1895 gun, bores ran on the large size then.... I haven't seen any info of original bores being under .729.... so if not close to factory where was the metal removed?
These are decisions each individuals will have to make but I think the gun has to be looked at and assessed.
Rich, we have a smith in the area that apprenticed and worked in England and he has mumbled numbers in that area.

surly those barrels on parkers struck at 3 lbs and under has to be pretty thin...a gun weighing 6 lbs and under cant be very thick or it will start weighing more trhan 6 lbs... just my opinion..... charlie