doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com LUP equates to PSI?

Guess we shouldn't get worked up about the pressure disparities. SAAMI allows the maximum average pressure for 2 3/4" and 3� shotgun shells to be 11,500 PSI +/- 900 psi, with the maximum extreme variability not to exceed an uber-max of 12,500 psi +/-900 psi or 13,400 psi

Darned Brits. There they go again! The first table refers to "velocities over 120 feet" (40 yards)--which is why those velocity numbers are so low. I knew that they were using something called "observed velocity" (average velocity over 20 yards)--which shows up as recently as 2005 in my "Eley Shooter's Diary". But they also sometimes use true muzzle velocity (at the muzzle as opposed to our 3 foot velocity figure . . . typically about a 100 fps difference.) But I've also found reference--in a BASC Information Sheet on "CIP Regulations on Steel Shot Ammunition And Shotgun Proof" to: "Mean velocity, measured at a point 2.5 meters from the muzzle . . . " So now, in addition to those 3 different "modern" methods of measuring velocity, we now have to remember that if we see something really old from the Brits on velocity, it's the average over 40 yards . . . which clearly means that those loads aren't nearly as slow as we might think.

I believe those velocities over 40 yds are US figures. For many years in the US, shotgun velocity was stated this way. The Brits used the observed velocity over 20 yds from way back. This was at times converted to Muzzle Velocity. The early chronographs which marked a dropping rod simply required a longer time interval for accuracy so velocities near the muzzle were not reliable.

And to further confuse us brainless Colonials, these MVs are what we would use today for the Dr. Equivalents

G.T. Teasdale-Buckell, Experts on Guns and Shooting, 1900
https://books.google.com/books?id=P7UrAAAAYAAJ&pg=PA235
1 1/8 oz. load comparisons. Pressure converted used Burrard�s formula
42 gr. = 3 Dram Bulk Nitro � 1� chamber pressure 7,985 psi / MV 1208 fps
45 1/2 gr. = 3 1/4 Dram � 9,730 psi / MV 1,274
49 gr. = 3 1/2 Dram � 11,780 psi / 1,328 fps

I still can't believe some guy at the Proof House just guessed at the Tons to PSI conversion!!

Except the pressure readings are shown in tons. Were we using tons for pressure back then? As best I can recall, I always saw US pressure measurements expressed as psi . . . before it was determined that psi wasn't really accurate and they started using LUP/CUP instead for crusher measurements.

And I'd thought that the Brits had dropped the "observed velocity" (avg over 20 yards) measurement . . . except my Eley Shooter's Diary from 2005 still refers to 1070 fps as "standard velocity" and 1120 fps as "high velocity (although they do give the metric equivalents of 325 and 340 meters per second, respectively.) You'd think, since they're in the shotshell business, that they'd be using whatever is the current standard measurement for velocity . . . if there is one.

True Larry, the tons pressure reading would normally make one think British. However, the 40 yd velocity measurement rings of the US as does the use of DuPont Bulk & Oval powders. These readings are from the 1920's & I do not recall having seen any British figures of that era with these powders or the 40 yd velocity. I am still going to have to go with them being US figures & just wonder why the pressure was stated in tons.

In a 1927 Western Cartridge Co. flyer "Super-X The Long Range Load" Capt. Chas. Askins described the 12g. duck load as 1 1/4 oz. with 38 1/2 grains DuPont Oval with a muzzle velocity of 1400 fps (SAAMI standard is to measure at 3 feet from the muzzle) and "over a 40 yd course 1000 fps"; with a breech pressure of 3 3/4 tons (or 11,480 psi by Burrard; 11,172 psi if X 2240 X 1.33)



The 1931 pressure curve was still Tons



In 1933 PSI

Drew;
I note in this chart it is stated that shells were fired in a multi-piston gun. No doubt the pressure was recorded at multiple points down the barrel & the curve drawn through these points. I had always suspected that was how the curves were derived, but this chart bears that out. That Ballistite load @ 4.9 tons is really reaching up to the limit, higher than some proof loads.

If that 1400 fps is true muzzle velocity (which is the way it reads), then it's probably something close to the Super-X formula, which delivers 1330 fps at 3 feet.