doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Smokeless in BP guns - min barrel thickness?

Sorry if the topic has been discussed before

Intro from Captain Obvious: Of course, we all know that 'if the gun has no nitro proofs it is not safe for use with smokeless powders'. This is a good rule of thumb, but the reality can be a bit more complex.

As you all know, at a certain time period between introduction of smokeless powders and nitro proof becoming mandatory, quite a number of guns were made which were intended to use with nitro powders, but didn't have the nitro proofs.

Also, as gunman said in the recent Wm Evans thread, a few guns even after mandatory nitro proofs were made for export or colonies with bp proof only. Yet, if we're talking about a mass maker such as Webley&Scott or Westley Richards, it doesn't make sence to save on nitro proofs and increase the cost by changing the 'regular' barrel conifiguration, so these guns were probably just the same, only minus the proof marks.

So, there is a number of guns, which, for this or that reason, are OK to be used with nitro powders, even though they don't have the nitro proof stamp.

The question is, how do we tell?

What's the barrel thickness that a gun must have to withstand nitro loads?

(of course, period nitro loads are meant, not modern hot loads, and of course, condition of the gun must be taken into a consideration)

http://docs.google.com/document/d/1LFnSG34k3mBhLEjEgU267wAlIa215MNVQZhIiY62Hx4/edit

c. 1895

"All bored for Nitro Powder"



"Guaranteed For Nitro Powders"

No one can wave a wand and say that they are all safe, whether the old gun has proof marks or not. The gun is really not that smart and it is working under an amount of pressure that they were designed for. I do shoot ALLOT of Damascus. I try to stay at a PSI of no greater than 7000 psi. But, I cannot or will not tell you it is OK for you and your guns. All of us who try to control an explosion in our hands in front of our faces, all have to be willing to accept some kind of risk. Stay below the pressures your guns were designed for and that the barrels are sound, you shouldn't have a problem. I shoot Bakers, and all the ones I had were designed to shoot either Nitro or BP, again, depending on pressures.

"For Nitro Powder"

Interesting that so many American damascus guns, i.e., Smiths, Parkers, Lefevers, Bakers, Remington, etc were designed for both nitro and bp, while many continental guns were not. Not sure why that is, since the barrels for many of the American guns were imported from Europe.

Crescent in the 1900 Sears catalog "Bored for Nitro Powder"

Mt Thomas Bland and Sons 20 was nitro proofed in 1899 for 7/8oz loads.
I also used to own a greener that was sent back to Birmingham to be re-proofed for nitro.
Both are Danascus barreled guns.
Mostly I shoot BP out of my Damascus guns, but do have some low pressure loads I use as well on the skeet field.
For hunting I use BP however.
DT

My Greener Emperor was made in 1894 and bears only the single provisional Birmingham proofmark on each barrel. The gun was never retailed and remained with Greener until the last remnants of company were sold in the mid '60s. The minimum thickness on the laminated barrels is .045". The bores are perfect. I use RST shotshells with no worries.

Thank you, Rounsworth.

I believe, however, that minumum wall thickess has not much to do with the matter. Apparently, it is the chamber area where the walls had to be made thicker to withstand nitro pressure.

So, the measurements I'm looking for are 1) at the breech; 2) at the end of chamber; 3) at the end of forcing cone.

This is especially relevant for the guns which had the chamber lenghened - you've got to know if there's enough wall left, but how much is enough?

Per the link, the least wall thickness recommended by CIP for 'standard steel' at the end of the chamber is .079" and just past the forcing cones/4" from the breech .075".

Courtesy of Hugh Lomas for English 12 bore game guns with pre-1925 proof:
Chamber Immediately prior to Forcing Cone - .105"
Post 1925 proofs - .100"

Also see http://parkerguns.org/forums/showthread.php?t=1565&page=4