Barrel Wall Thickness

[clumber]

What wall thickness would you be looking for in a 12 gauge shotgun chambered for 2 inch cartridges?

I was told a long time ago (right or wrongly) that the trade consider 18 thousandths as the final thickness of barrels, 2.5" chambers, that have normal 950bar pressure.(20 thous being preferred)

With the 2" being a lower pressure would the wall thickness be thinner and the barrels shorter to make the gun lighter along with a lighter action? OR is the 2" tested at 950bar and making my information utter codswollop?

Had a look at the proof house but can't find thickness's or pressures for 2".

Any help from PW oracles would be appreciated, cheers, clumber.

[subsonicnat]

I think you asking them to put their bums on the line there mate..

[Andy135]

Presuming your gun's barrel wall thicknesses are marginal (otherwise you wouldn't be asking). I'm with subsonicnat, it's unlikely that that anyone will give you a definitive answer as it all depends on each individual gun and how it's been treated in its life. But why take the risk? If it has sentimental value either get it sleeved or deactivate it and use it as a wall hanger.

 

If it's a gun you're thinking of buying I'd walk away. Plenty of good guns around without thin walls to choose from.

[clumber]

Cheers for posts but I think I didn't come across right. What I'm after is were 2" chambered barrels made lighter and thinner, IF they had a lower proof pressure? or would they have been made to the same spec as 2.5" chambered barrels at 950 bar pressure?

I've been told about a gun with 2" chambers but the info given about the barrels being made thinner, I believe is wrong.

Hope this is a little clearer, cheers.

[deershooter]

I have a side by side hammer with only 17 tho in the right barrels only black powder proof I won't submit for proof or shoot it

Edited October 23, 2015 by deershooter

[Stonepark]

I suspect. Pre modern proof Other than in possible custom exceptions or experiments. There will be no difference between normal barrel thickness between 2 and 2.5 inch as gun makers could not accurately measure pressure without a good margin of error and a lot of guns were marked up for BP proof.

 

However it is unlikley they would survive a NP proof.

[JohnfromUK]

A lot of older English guns were quite thin even when new. There are many factors; wall thickness near the muzzle is not required so much to resist internal pressure, but to resist dents and damage. I think it was Greener who experimented with guns wafer thin near the muzzle - without bursts. However guns below 20 thou dent more easily and each dent removal looses a little more metal.

 

So called 'best' guns with fine balance had the barrels very carefully struck up leaving plenty of wall where the pressures were high - and saving weight where the pressures were lower - thus keeping the weight between the hands. It seems likely that 2" chambered guns, designed to be light and fast handling (as well as having lower pressures) would have been a little more thinned and perhaps to a slightly different profile - but not to the extent that they dented easily.

 

As I'm sure you know, proof is about the change in dimension since last proof - not absolute dimensions. I don't believe wall thickness is measured - only bore diameter - and that only 9" from the breech. I may not be fully up to date here - so please someone step in and correct if I'm talking nonsense! For a 12, originally proved as a 12, that would be a nominal 729 thou bore. The gun would go out of proof from any alterations (e.g. chamber alteration) or when the bore had been enlarged by 10 thou (or more) - i.e. measurement exceeds 738 thou.

 

20 thou as minimum wall thickness is often advised as a practical minimum, but some think below 25 thou reduces value.

[Gunman]

Many 2" and lightweight barrels left the maker with walls under .025" . Bearing in mind that measuring equipment was a lot less sophisticated when they were made and barrels were stuck up by hand it is not uncommon to find original barrels with walls of less than that .

Under CIP rules of proof [ and I will not get on my hobby horse of how stupid they are ] there is no provision for 2" proof so the gun if submitted would be treated as a 2&1/2" or 2&3/4" with the same proof pressures . I have recently had this argument with the Proof House and as a result I will not send any 2" gun for reproof . It is not only the barrel but the lightweight action that is likely to fail .

The much talked about "minimum wall thickness" is a invention of auction houses and taken up by many dealers ,especially when buying , to enable them to sell guns that are basically worn out without come back as the purchaser is aware of the barrel condition .

There has never been a minimum wall thickness set down by either makers or the Proof Houses .As far as the Proof Houses are concerned a gun is submitted at the submitters risk and only firing will tell if a barrel will pass or fail .

It is also a fact that as there have been different steels used that modern steels may require less wall thickness that those used in the earlier 20C . It was held belief in the Birmingham Trade that you needed .010" more thickness on a Greener barrel tube than that of one by Webley for example .So the "minimum" would be different .

Biggest problem is that the thinner the tube the less likely it is that you can remove dents or other damage without making the gun unsafe .