It frequently happens that during the process of rescuing an old gun from the scrap heap, one has to consider the risky business of submitting it for re-proof.
All guns offered for sale in the UK bear marks stamped on their barrel flats indicating that they have been tested and proven safe to use with cartridges of given pressures. The law is a sensible one as anyone buying a gun at any price can be assured that it is fit for purpose and will not fail under normal use. It prevents unscrupulous traders selling shoddy goods that would be a danger to the public.
Once stamped, the proof marks are good for the life of the gun as long as it is not altered or weakened beyond certain tolerances. However, once those tolerances have been exceeded, the gun must once again be prepared and submitted to a proof house and subjected to a test of strength.
When pits are lapped out of the bores and the bore size subsequently increased to become more than ten thousandths of an inch larger than when originally proved, the gun must be re-proved before it can be legally sold.
Incidentally, always check auction guns that have been recently re-proofed by the auction house. There is something of a tendency to do it as quickly and cheaply as possible so dents are not always raised and the lapping tool is all too frequently pushed right through, resulting in all choke being removed from the muzzles.
‘View’ is a visual inspection by the Proof Master. If he thinks the barrels not sufficiently tight on the action, or he notices dents, pits or other faults, he will reject it as unsuitable for proof. If he considers it in good enough condition, it passes ‘view’ and goes on to be submitted for ‘proof’.
For this purpose, the stock is removed from the action, to avoid damage and the barrelled action is subjected to two proof loads in each barrel. The proof master then gives a visual inspection and checks to see that it is still tight and that the barrels have not bulged, or otherwise changed, due to the pressure of the proof loads. If he is satisfied, the new proof marks will be stamped on the flats, showing the new bore size, the pressure for which the gun is now proved and the chamber length.
One needs to be careful when preparing old guns for re-proof. There is always a risk that old barrels, thinned by honing and weakened by pits will ‘move’ when the proof charges are fired. If they do, the proof marls are struck off and the gun will have to be sleeved.
Reasons a Gun May Need Re-proof
Chamber lengthening. Americans are the usual culprits. A gun comes back from the USA, where the owner has decided he wants to shoot American shells in his English gun. American shells are longer and more powerful so he has his local gunsmith extend the chambers so they fit. When it arrives back in the UK for sale, the British gun dealer realises it is illegal to sell because it is legally ‘out of proof’ now. Before it can be sold it must be submitted for proof and stamped as having 70mm chambers.
Screw-in chokes. The fixation some shooters have with choke continues and some decide they have to have screw-in chokes of the Teague or Briley type fitted to their old sidelock. If they do, it must be re-proved, as the law deems this a material alteration which could affect the strength of the barrels.
Bore size. If the bore becomes enlarged due to repeated cleaning out of rust or pits, the gun stays ‘in-proof’ until the enlargement reaches ten thousandths of an inch. Then it has to be re-proofed.
Nitro for black. Black powder proof marks remain valid but it is recommended that guns with black powder proof be re-proved if the owner wants to use modern nitro ammunition.
Reasons a Gun can Fail Re-proof
Rivels (small ‘waves’ left in the metal where it has not sprung back into shape)
Bulges (bigger areas of expansion, usually where the metal is thin)
Cracks (in the chambers, action or lumps)
Coming off the face (the barrels must still be tight on the action after proof)
Lumps (dovetail lumps can become loose or even detach)