doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Pressure graphs

Many thanks to Pete Lester on the PGCA site for calling attention to this from Sporting Guns and Gunpowders: Comprising a Selection from Reports of Experiments, and Other Articles Published in the "Field" Newspaper, Relative to Firearms and Explosives, Volumes 1-2, 1897
http://books.google.com/books?id=inQCAAAAYAAJ&source=gbs_navlinks_s

p. 32 Powder Pressures At Different Parts of the Gunbarrel, 1895
http://books.google.com/books?id=inQCAAA...ure&f=false
(scroll down and click on p. 31)

Using the estimate Lead Crusher Pressure (Cp) conversion to PSI (pound force per square inch)
(Cp x 1.5) - .5 = TSI, TSI X 2240 = PSI

32 Gr Ballistite (1 1/8 oz at 1232 fps muzzle velocity = 3 Dram Equiv.)
Breech - 2.9 Tons per Square Inch (UK, Long) = 8624 psi
(2.9 x 1.5 = 4.35, 4.35 - .5 = 3.85 TSI, 3.85 x 2240 = 8624psi)
2 1/2" - 2.2 Tons = 6272 psi
6� - 1.2 Tons = 3718 psi
12� - .81 Tons = 1602 psi
18� - .33 Tons = 1120 psi
24� - .21 Tons = 694 psi

83 Gr No. 4 Black Powder at 1222 fps
Breech - 2.26 Tons = 6474 psi
2 1/2" - 1.96 Tons = 5466 psi
6� - 1.26 Tons = 3114 psi
12� - .9 Tons = 1904 psi
18� - .37 Tons = 1232 psi
24� - .27 Tons = 896 psi

SO once again, the pressure is falling rapidly with either Black Powder or Smokeless and is quite low by 18"

This might also be of interest "Long Cartridges in Short Chambers"
http://books.google.com/books?id=inQCAAA...ges&f=false
(Click on p. 83)

1875 and 1888 Trials of Cylinder and Choke Bores
http://books.google.com/books?id=inQCAAA...ore&f=false
(scroll down and click on p. 61 and p. 105)

It's all relative sez Einstein.

739 psi is low compared to chamber pressure, but it's still 50 atmospheres.

It requires serious containment.

Note that those are almost certainly not true PSI figures. If they are British Crusher pressure the 2.9 would be on the order of 8600psi & the 2.26 around 6500psi. It is interesting that both powders had the same pressure at 18" point while the black was higher (As Expected) at every other point beyond 2�".

"If they are British Crusher pressure the 2.9 would be on the order of 8600psi & the 2.26 around 6500 psi."

You are correct Miller. I used the only conversion table that I could find. Do you have a better conversion?

And another graph
"The Proof of Guns with Fine-grain Powder"
http://books.google.com/books?id=inQCAAA...ER.&f=false
(scroll down to p. 225)

Drew;
The figures you quoted are correct insofar as converting tons to pounds. 2.9 tons times 2240 lbs per ton gives the 6496 lbs. It is thus correct to say those loads gave 6496 lbs of crusher pressure or LUP. Burrard reported that a series of tests were run after the Piezo Electric crystals came on the scene which record actual PSI using a pressure bbl set up with both methods measuring pressure simultaneously. A "Workable" conversion which would give extremely close readings over pressure ranges normally encountered in shotguns was found.
Leting Cp = crusher pressure the formula was as follows (Cp x 1.5) - .5 = TSI. Thus 2.9 x 1.5 = 4.35 4.35 - .5 = 3.85 TSI.
3.85 x 2240 = 8624PSI. This would not be exact, but very close.

Can one of you reconcile what I read from Doug's post a few months back, regarding "long ton axial"?

http://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=297079

From the listings in all my various old ammo catalogues from the first decade of the 20th century, 32-grains of Ballistite would be a lot more that 3 drams equivalent. The heaviest Ballistite 12-gauge loads offered, at least from 1903 on, were 28-grains pushing 1 1/4 ounces of shot out of a 2 3/4 inch or longer 12-gauge shell. According to a couple of DuPont powder books I have 28-grains of Ballistite pushing 1 1/4 ounce of shot in a 12-gauge peaked at 12600 pounds!!

One could get 32-grains of Ballistite in a 2 7/8 inch 10-gauge UMC Arrow shell pushing 1 1/4 ounces of shot, and that would be the equivalent of 4 drams of bulk smokeless and 1 1/4 ounces of shot.

The load was 1 1/8 oz. at 1232 fps, but was muzzle velocity rather than 3 feet as SAAMI measured.

I corrected the conversion numbers on the original post and thanks Miller.