doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Cracking action

Americans put down serious money for guns out of proof every day. A hundred bucks will buy an excellent bore micrometer and another hundred will buy an excellent wall thickness gauge that will tell the buyer more about a gun than any proof mark. A proof mark will not tell you how many times the barrels have been struck since the marks were applied.

I think a bore micrometer, wall thickness gauge and chamber gauge are very important and useful tools. I own all three and find them great for analyzing these shotguns, specifically for evaluating whether a gun is 'in proof'. I also think they give an estimation of a gun's safety, but stop short in comparison to actually proofing a gun. These


tools, or instruments are very helpful to the knowledgeable gun person. However, Most Americans who have guns, don't have a clue what a barrel wall thickness gauge or a bore micrometer is, let alone how to use one or understand the data they generate. Just my humble opinion, but I only buy guns which are in proof, if I can help it.

ACTION FLATS


ACTION FLATS


ACTION FLATS

Yep,you're right, the proof mark won't tell you the wall thickness, you'll know if it's been re chambered or been honed to near death though.
We have our hands tied over here. It's not only bad practice but more importantly, against the law to offer for sale a gun that is out of proof. Barrels are often measured many times before a sale. The buyer may want an independent gunsmith to measure them for peace of mind so yes, it is important.
The point I was aiming at with the original question was even if the old barrels prove strong enough, could the action suffer from the repeated use of nitro ?

Major ,Sir Gerald Burrard,covers the issue of," cracked actions"in his book;The Modern Shotgun.Vol,The Gun,1 pages 73-82.Vol;3,The Gun and Cartridge,pages,401-403.Burrard compares the physical strength and properties of various side lock and boxlock actions.
He recommends boxlock guns be fitted with a top rib extension with a reliable 3rd,fastener in order to minimise the risk of action cracks!
Burrard illustrates the adverse effects of over-heating of the action on the physical properties of the action metal.Ilustrated is the microstructure before and after excessive heating and the cracked action that resulted from over heating!
Burrard also stresses the need for adequate metal thickness of the water table and the need for a corner radius at the junction of the water table and the breech face so as to avoid stress concentration so as to minimise the risk of action cracks.
He expresses minimal concern over pin holes drilled on or near the neutral axis of shotgun actions as they are unlikely to act as stress raisers.
Burrards work on the analysis of shotgun design is still the most comprehensive design review available and is recommended reading.

As a practical measure, the gun still measuring within its proof limits assures a buyer that it is safe to use with the loads proofed for.

Of coures, you still need measuring tools to see if the barrels are within prof limits.

I once had a Grant sidelock crack at the radius. I have a nicely cracked Cogswell & Harrison boxlock action here as well.

Weakening the metal through amateur attempts at re-colour hardening has always been one reason I dislike it.

We can all look at a gun and opine on if it is or isn't likely to be safe.

Proof tests our opinions and tells us to what tolerances it actually is.

Prof is not a legal requirement in the US. That does not mean it does not matter to Americans. A lot of my American clients are very aware of it and careful to insist guns they buy are in proof. It certainly affects price.

That said, I reluctantly re-proof guns. Proof subjects them to severe stress. Don't do it unless you have to.

I'm using Birmingham for re-proofing at the moment. London are bulging barrels at the muzzles again. Of course, they always deny anything is wrong when a spate of guns start to fail out of all reasonable expectation.

The one thing I would add to Roy Hebbes post above is the additional factor of the steel which was used to make the action. Take a poor, or weak, or marginal design that might otherwise last for hundreds or thousands of shots before wearing out or becoming loose using the correct conventional ammunition... and make some of those same actions with a batch of steel that contains slag inclusions, porosity, contaminants, or slightly incorrect alloy... and now you've added the straw that broke the camel's back. Even today, with state of the art metallurgical labs, flawed or out of spec batches of steel sometimes make it out the door and get to the customer. That's one reason why some brand-new, unfinished barrels fail initial proofing. Experts say bad steel is the reason the Titanic went to the bottom of the ocean instead of limping into New York harbor with a big dent in it's side.

Small Bore
Many years ago whilst in Birmingham, I enquired at a respected gunmaker their cost to recolour hardening a gun action.The reaction of the gunmaker was to produce from storage the cracked action of a Boss sidelock[1 of pair] that had been re;case hardened and then submitted for reproof.The gun action cracked at proof!
Nothing to do with the barrel dimensions!I was told by this gunmaker that they would not re;case harden a shotgun action unless the gun was resubmitted to proof after hardening.Further more the owner authorising the work was required to sign a waiver holding them harmless if the gun action should fail at proof.
Based on this example, I have never again considered re;case hardening any of my guns.

Roy, I had the same advice from one of Canada's best gunsmiths. I followed it, of course.

Strange how London seems to bulge barrels with cartridges loaded in Birmingham .