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I am confused about a certain aspect of proof marks. Tons and bars I assume refer to pressure which makes sense to me. But what does the shot load have to do with anything? Why specify
1 1/8 oz or some other shot charge? What difference does it make how much shot is used in a particular load if the type and amount of powder used does not generate excessive pressure?

Richard,

Think about if for a moment. Say you load 3 drams of black powder in brass shell. No wad, no load. You ignite the shell, the powder burns off. Take the same shell and seal it. What happens when you ignite it? The pressure causes the shell to rupture. This is what happens when an obstruction causes a barrel to burst.

Many things can increase pressure. The load going down the barrel encounters friction. The more friction the higher the pressures. So wads play a factor as does the weight of the shot being pushed by the gases.

Pete

DE of BP plus shot load is a "sorta" surrigate for pressure. Also, Brit loads tended to go to longer cases with increasing shot load. When you consider DE and case length tied to shot load, then shot load becomes an indicator of the pressure and power of the gun. Keep in mind that pressure measuring was a rare event until recently. Shotgun proofing has its roots before pressure was well understood and easily measured. Now days, shot load is one indicator of recoil - important to gun wood and the shooter.

Good synopsis there R'Mam. I would however point out a few things. DE (Drams Equivelent) was a term which came into being with Smokeless Powders, Black Powder was measured in actual Drams (1/16oz). The DE was used to designate an equivelent power (Velocity) not an equivelent pressure. Loading a 3 Dram load of black behind 1 1/8oz shot & a 3 DE load of say Schultze for a similar power level (1200fps) would not give the same max chamber pressure, as the Schultze was faster burning than the black. The early Bulk powders were measured to an equal "Volume" with Black of same power level, but not weight. DE came into use primarily beginning with the widespread use of "Dense" powders as both the Weight & Volume was difernt than black for a similar power level. Marking the shot weight was instituted I believe in 1896 on British proof for guns given the voluntary smokeless proof & both max powder charge wt (Smokeless, usually bulk) & shot wt were marked. This continued until 1925 at which time the actual powder wt was dropped & was simply marked Nitro & a shot wt. It was not until 1954 they upgraded to an actual pressure measurement, though Greener had spoken of the Crusher Gauge at least as early as 1911. The marking of the shot wt had led to some confusion among users as the suitability of a load was determined, not by actual shot wt, but by max pressure developed. Special low velocity loads for the 2½" gun had been developed using 1¼ oz shot but many felt using these "Took the Gun out of Proof", which was not the case. This situation was rectified with the 1954 Rules of Proof.

Jules Polain became the director of the Belgian proof house in 1890.



He immediately starting experimenting with ways to measure pressure.





This was a 1909 result.


The actual proof room in 1909.


1899, apprentices (with aprons) and young runners waiting for the proof house to release barrels and guns back to the makers. The proof house can be seen in the background.


Pete

So, all else being equal, a 2 1/4 oz load will produce more pressure than a 2 1/8 oz load?
The shot charge stamp on the barrel flats is part of the description of the working pressure?

Good catch, 2-p; I was thinking drams and typed DE. Thanks.

RH, yes, for practical purposes you can assume that all else equal, an increase in shot load will produce an increase in pressure. A 1 1/8 oz proof would indicate a 2 1/2" shell, 1 1/4 oz would be 2 3/4", and 1 1/2 oz would be 3"; the stated shot load was typically the maximum load for the stated hull length.

It is governed to a large extent by the physics formula F=MxA where force equals mass times acceleration. When max shot charge was used to denote proof level powders were pretty much standardized in terms of burn rate resulting in similar peak pressure and overall pressure curve shape. Thus if the mass is specified i.e 1.125 oz, the accelaration is pretty much a given (at that time) say 1200fps then the force applied to that mass to accelerate it 1200fps at muzzle would tend to be constant. The force is the product of the area under neath the pressure curve, as powders then had fairly even burn rates peak pressures would fall within a safe band. It began to fall apart with the introduction of shells like Eley Maximun which had 1&3/16th oz shot but were safe in 2&1/2" guns marked 1&1/8th oz max. They acheived this by modifying burn rates to lower peak pressure but extend the elevated portion of the curve further down the bore.

Very interesting. I'll rush home and check the proof marks on my Army & Navy which was opened to 2 3/4 before being sent to the London Proof House. Should say 1 1/4 oz. I gave my Bozard to Toby Barclay at the Southern SXS to take back to England for work including 2 3/4" chambers and reproof. As I recall, it was stamped 1 1/8 oz. So it should come back stamped 1 1/4 oz (assuming it survives).
They are both damascus.
The reason I asked this question is the first place was because I have been trying to determine just how much pressure, in PSI, the old girls will take. Tons and bars are too mysterious to me. To be safe, I load WinAALite and 7/8 oz of shot at 1050 FPS and 5500 PSI. But I really should understand proof marks if I'm going to keep buying these ancient fowling pieces.

Richard,



This topic has been discussed before:
http://www.doublegunshop.com/forums/ubbt...=true#Post61404

Pete