doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Question for Drew...

Again from the Birmingham Proofhouse: 3 tons = 8,943 psi (approximate conversion to CIP transducer measurement). 4 tons = 11,913 psi. That's about the same difference that the Birmingham Proofhouse gives as the current spread between service pressure of an 850 bar gun (10,730 psi) and proof pressure of said gun (13,920 psi). Looks to me like somewhere along the line, service pressure and proof pressure got mixed up.

Actually Tom, an oscilloscope would have been pretty hard to use on a non-repetitive event like this, especially in those days.
Other equipment were usable (e.g. chart recorders) but probably nowhere fast enough to be useful.
The advantage of the crusher, is that it has memory and removes this issues. It is also slow and distorts the results.
It is hard to grasp how some measurements were oh so difficult to make, not so long ago.
WC-

larry;
You just made my point exactly, though I think it was accidental. if you check back over what i have been saying Mr goddard did in fact give "Both" service & proof pressures. for the 2 5/8" chambering he gave the service pressure of 4� tons (9500 lbs) & the proof pressure of 6.1 tons (13,700 lbs). This pretty well eliminates the possibility that he mistakenly recorded the proof pressures for the Service ones.
My main point however has been the pressures he listed simply do not mate up with the LUP's of British pressure of the era, but do very closely match what we now know as actual PSI's. As to exactly how he derived these pressures I do not know, but I think it imperative that we realize a gun proofed under these parameters "WAS NOT" proofed for a service load of 4� LUP tons. This would actually be in excess of our modern SAAMI Spec loads.

Ballistite maximum pressure at 1� was 4.9 Long Tons = 15,344 psi
Schultze at 1 1/2� was 4.5 Long Tons = 14,000 psi

"When this chart was published in the American Rifleman (minus the Ballistite Curve) in the 1950's they stated the load was a 3 dram or equivalent charge with 1 1/4 oz shot."

I believe AR was mistaken

From "Smokeless Shotgun Powders: Their Development, Composition and Ballistic Characteristics" by Wallace H Coxe; E.I. du Pont de Nemours & Co., 1933. Pressures reported for a 3 1/2 dram equivalent 1 1/4 oz. load:
DuPont bulk smokeless powder - 11,700 psi
Schultze bulk smokeless powder - 11,800 psi
28-grains of Ballistite - 12,600 psi