doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Wall thickness measurement

A very helpful pressure-distance graph dated June 10, 1929, from the McCracken Research Library, Buffalo Bill Center of the West (found by Gary Rennles) and used by permission
http://library.centerofthewest.org/cdm/singleitem/collection/WRAC/id/8149/rec/107

The digital image is part of the Winchester Repeating Arms Company Collection but includes a notation “Hunter Arms Co”. WRAC was acquired by Western Cartridge Co. Dec. 22, 1931, so it is impossible to know if the curve was generated by Winchester, Western, Hunter Arms, or (very possibly) the Burnside Laboratory of the E.I. du Pont de Nemours & Co.



PROOF LOADS
Loaded with FFFg black powder. Shot presumed to be No. 6.
Pressures were measured by crushers (LUP - Lead Units Pressure) and modern piezoelectric transducer measurements would by 10 – 14% higher
F - 10g 2 7/8” 9.5 Drams with 2.36 oz. shot = 16,000 psi
A - 12g 3” 8.265 Drams with 2.187 oz. shot = 17,250 psi
G - 12g 2 3/4” 7.53 Drams with 2 oz. shot = pressure not recorded
B - 12g 2 3/4” 6.5 Drams with 1.687 oz. shot = 14,200 psi
C - 16g 2 9/16” 6.5 Drams with 1.687 oz. shot = 13,750 psi
It seems likely the ‘B’ 12g and ‘C’ 16g labels were switched
D - 20g 2 3/4” 5.74 Drams with 1.5 oz. shot = 14,625 psi
E - .410 2 1/2” 2.377 Drams with .624 oz. = 15,625 psi

MAXIMUM STANDARD LOADS
1” peak pressures
H - 12g 3” ‘Record’ 1 3/8 oz. shot presumed 1275 – 1295 fps = 13,250 psi
I - 12g 2 3/4” ‘Field’ 1 1/4 oz. shot presumed 1330 fps = 10,750 psi
The label ‘J’ for 28 gr. Ballistite and ‘K’ for 3 1/2 Drams DuPont Bulk appear to have been switched on the pressure curve graph. Dense Ballistite clearly generated greater pressure than DuPont Bulk.
K - 12g 2 3/4” 1 1/4 oz. 28 gr. Ballistite = 12,900 psi
J - 12g 2 3/4” 1 1/4 oz. 3 1/2 Drams DuPont Bulk = 10,000 psi



The pressure curves essentially meet at 5” at 7000 psi; at 10.1” 2625 psi (DuPont Bulk) to 3000 psi; at 15.5” 2000 psi; at 22.1” 1500 psi



More vintage pressure-distance curves are at the bottom here
https://docs.google.com/document/d/1F2sQuPm05IE4VWYYnCkvuXmYEzQoWd_SQgaAfUOZEFU/edit

Well Stan put a pump on your tractor that doubles or triples the pressure I think double charge of incorrect powder will cause problem for a gun I have seen a fox blown up because of this exac problem to much pressure barrel gave it up

I've seen them blow, too, mc. But, overcharges blow the chamber out, not several inches down bore, IMO.

Unless the overcharge pressure doesn't drop enough and the wall thickness decreases enough to have a catastrophic failure. I never say never when s**t happens

.012"? Well sure. I should have qualified my belief by stating I was referring to something reasonable. What's reasonable? For one, what it left the manufacturer with.

Beyond that, what's reasonable for me may not be for you. I am only responsible for my decisions about this. There are limits to everything. I'd like to see that engineer if he were to be confronted with a chamberless, barrelless gun about to touch off a round. I don't think he'd be standing beside it. I wouldn't, obstruction or no.

I'm still not convinced that Perazzi had no bore obstruction. Show me proof it didnt. Why would that pressure blow through .012" high tensile steel alloy when it could exit down bore?

Without a bore obstruction it has to drop, quickly. Until a powder is developed that doesn't build peak pressure in the chamber, that's they way it works. A random shell can't create new laws of physics.

I can absolutely believe a barrel with walls .012 thick could burst, and it probably wasn’t from a bad reload or obstruction. Remember, an aluminum soft drink can is .005” thick. I’d like to know what the factory bore diameter Is and what it is now with the overboring. I bet we’d be shocked at how much metal was removed from those bores

Even if you know those two numbers, you do'ng know that it was concentric without actually measuring the thickness directly. Who is to say that the overbore was concentric at all points along the way?

You can be certain it didn't leave Perazzi like that. Perazzi goes, what might be considered by other manufacturers, overboard with barrel testing. They do a destructive test on one of every 50 barrels, hydraulically bursting it to determine psi needed to do so and location of burst.

Here is the original thread
https://www.trapshooters.com/threads/perazzi-barrel-blew-up.433985/

Another thin wall split; honed to .739" with wall thickness .018". I don't know the load that was being used, but there is no ring bulge to suggest an obstruction