doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com British Proofing - Tons to PSI

Hi all, whats the formula to convert Tons per square inch to PSI?

Can't seen to find it, of course - I'm slow today!

Thanks!!!

Greg

Please see http://www.16ga.com/forum/viewtopic.php?t=3428
and thanks to Larry Brown

Per the 1954 Rules of Proof, here are the equivalent service pressure values:
3 tons--8,938 psi
3 1/4 tons--9,682 psi
3 1/2 tons--10,427 psi
4 tons--11,917 psi
These numbers SHOULD apply to guns proved under the 1925 rules, which were stamped only with chamber length and shot charge. Thus, a 2 1/2" chambered gun, 1925 rules of proof, would be equivalent to 3 tons; a 2 3/4" chambered gun to 3 1/4 tons.

A service (using) pressure of 3 tons per sq. in. = 8,938 psi service pressure (SAAMI) BUT please keep in mind that pressure does not equal recoil (which is a function of shot charge and velocity.) Pressure stresses the action, recoil the wood (and the shooter.)

Thanks Rev. just what I wanted...........your great!!

All the best!!

Greg

Perhaps this is a stupid question since I know little about proof standards and procedures, but I'll ask anyway. Does psi/tons convert or have a direct relationship to a gun marked as proofed at a load of 1 1/4 ounces or 3 1/2 ounces of shot? Is there a relationship at all?

Very early in the "proof system" measurement was done by load.


To standardize across various lots, they developed tools so that they could precisely measure the load.


Proof by pressure was a latter development.


That eventually became the piezo method we know today.


I think you already know the answer to this one. If I load a shell with 1 ounce of shot and 40 grains of IMR4350 do I get the same pressure as if I loaded it with 40 grains of Blue Dot? No, because pressure is dependent on the burn rate as well as load. Which was why they had to develop the tools pictured above to standardize the loads between lots.

Pete

The Ton used in British proof was 2240lbs. Thus tons x 2240 is a direct conversion from tons to pounds. What is "NOT" a direct conversion is crusher pressures to piezo-electric pressures which are considered to give true PSI. In the early days of working with the piezo-electric pressures bbls were set up with both P-E & crusher gages & simultaneous readings taken at the same 1.0" station. A "Workable" formula for conversion, within the normal pressure range of shotgun bbls was found to be;
P-E (tons) = (Crusher tons x 1.5)-.5 Multiplying this figure by 2240 will then give psi. Note that this formula was not given to be "Exact" but to give reasonable working pressures. By working through the pressures given per the Birmingham proof house & comparing the greatest difference will be found to be on the order of 3% & this on the 4ton pressure, the other 3 being from 2% down to near zero. The reason for the differences & why no exact formula can be given is because of the varible "Lag Time" in crushing the piston. Within this range crusher pressures will always read less than the P-E pressures.