doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com proofed

Why are shotguns listed as "proofed" for 1 & 1/4 ounce loads? Couldn't the pressure vary considerably between two different loads, or am I missing something. I suppose this is a pretty basic question, and I never really cared when I just had a 870 Wingmaster. Bur I find my interest taking me to the doubles these days and want to understand everything I can about them.
Thanks for the help, and patience.
Gary

The shot load is an important factor in required strength of the gun. Shooting purpose and shot charge weight are joined at the hip. The 1 1/4 oz proof is for pigeon/duck/high phez guns, where as 1 1/8 oz is for game guns (we'd call them upland bird guns) and the 1 1/2 oz is for fowlers.

Pressure is not defined by shot charge weight; influenced, but not defined. Note that CIP (European) pressures are standardized at lower values than are SAAMI (USA) standards.

A light shot charge in a high pressure loading can be damaging/cyclic life shortening to heavy proofed gun's actioning. Likewise, a heavy shot charge low pressure load can be damaging to the wood of a lighter gun. Match pressure to the metal and recoil to the wood.

For older doubles, think in terms of light shot charges (3/4 - 1 oz), low pressures (5000 - 7500 psi), low velocities (1050 - 1200 fps), and a service/repairs warchest.

Sir Gerald Burrard discuses this at length in his "Modern Shotgun". The shot wt was a mark found primarily on guns proofed in England. 1 1/8oz was for 2½" chambered guns & 1¼oz for 2 3/4" chambered guns which carried a higher pressure than the 2½" guns. Shells were loaded in both lengths with hevier shot loads specifically for the guns they were to be used in, as the 1¼oz "Low Velocity" load in 2½" shells. This caused much confusion among users as many assumed the gun was not proofed for the shells. This was the primary reason for changing to the "Tons" mark rather than shot weight. Actually each shot wt proof had a specific pressure it was proofed to, which was the determing factor, rather than actual shot wt.

Please see this thread
http://www.16ga.com/forum/viewtopic.php?t=3428

Gary,

You are correct. It is confusing because you are not seeing the other component in the equation, the powder load. The proof houses had an agreed upon powder charge of black powder that was used. Even various lots of black powder could vary (for the stringent requirements of proof), so they would test the lots to determine how much powder would equal their normal proof load. Here are several devices for testing powder, from the Liege proof house dating from the 18th and 19th century.


Confusion came in with the advent of smokeless, nitro, powder. There was a brief period when various smokeless powders could be chosen for proofing a firearm. Eventually they centered their load development on pressure. Again, an early device from Liege. This 1895 device uses the crusher method.


The above are from Claude Gaier's "L'Epreuve des armes à feu à Liège, 1672-1972"

Pete