Proof firing

[scharfschutzen63]

I just happened to check. I have a no4 and a no5 enfield. Both are proofed 18.5 tons per square inch.
Enfield 7.62 barrels are proofed at 19 tons.
This is only 1000 psi more I am thinking. This is not much in relation to the overall pressure, but could still be beyond the failure point for a part that passed the 18.5 ton proofing.
19 tons per square inch is 38000 psi. In metric tons, just under 42000 psi
SAAMI Spec for 308 Win is 52000 cup.
I am thinking the units are different.
Can anyone shed some light on all of this?

Information

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[Peter Laidler]

My wife is a mathematician and pretty good at sums and especially good at counting and claiming expenses from work. But to be totally honest, she is out of her depth when it comes to the mathematical mumbo-jumbo that surrounds the mystical world of proofing. She says that it is all based on white mans magic and the phases of the moon in relation to the tidal equinox.

[Bruce_in_Oz]

It seems there are different "units", depending on the measurement method.

PSI, Megapascals, etc are one thing, but the method of estimating the pressure within a cartridge after ignition is interesting in itself.

If you see "C.U.P" in the description, that stands for Copper Units (of) Pressure. This involves a small cylinder of copper to be , literally, crushed by the pressure. It is used in proof and metrology labs to evaluate ammunition and to develop "proof' cartridges. The set-up is surprisingly basic. A HEAVY test barrel in a Mann rig has a small hole bored diametrically into the chamber, usually at about the half-way point.

This hole is for the copper plug, which is retained by a collar or similar. When the cartridge id fired, the pressure punches a hole in the brass case and then acts on the captive copper "plug" the result of this compression is measured and compared to data from plugs compressed hydraulically in carefully calibrated presses. It is a good "indicator" method.

A more modern method involves fitting a series of piezoelectric sensors. (pretty much "lab-grade" strain gauges), to the barrel reinforce and sometimes forward along the barrel. These give "instantaneous" readings as the barrel "stretches" radially at peak pressure. This is a complex process, but a rather "neat" system because it is non-destructive, unless the firearm under test is seriously defective. The techies crunch the numbers to arrive at a pressure figure.

Firing is usually done in a hardened room and the arms under test are often housed in heavy steel hoods, to catch the bits if it all goes wrong. The operators are usually in an adjacent room, firing by remote.

Final part of proofing involves the careful inspection of all "pressure-bearing" components to find any distortion or incipient cracks. REALLY good proof establishments also clean the tested arms to prevent nasty surprises when the owner opens the box, a few weeks or months down the road.

I reckon if you go to the SAAMI and CIP sites you will find more than you ever wanted to know about the whole business.

[nijalninja]

An old Lyman book I have details the differences in the two main processes for determining pressures, but I'm afraid I'll have to wait to tomorrow to read it and post up the wisdom. That is if its not already answered by then. From what I remember of it Bruce is on the money completely.

[CINDERS]

Yes the good old C.U.P measurements they used to use.........................just another one for the mix that Peter Laidler points out on the subject.

[Parashooter]

Do keep in mind that the traditional British system of pressure measurement employed an axial crusher, located behind a floating breech face and driven not by a radial piston but by the lubricated cartridge itself. The results are quite different from either the radial crusher system or modern transducer systems.

Remember also that the pressures marked on British-proofed arms are in long tons (2240 lb.).

[Paul S.]

She says that it is all based on white mans magic and the phases of the moon in relation to the tidal equinox.

Peter, that's the funniest thing I've read in a week at least. Thanks for the laugh Mate!

[Peter Laidler]

That reminds me Bruce......... We used to have a similar copper crushing method for testing the 'force of blow of the striker' for the old 2" mortar and some other equally obscure bit of kit........ I think it was the 1.5" signal pistol. You assembled this gadget with these copper cone shaped whatsits that had to fit whatever side up into the top half of the thinggy. But, alas, the EMER and every other booklet on the subject gave different points of view, depending if YOU were holding the contraption or whether the class teacher was holding the thing to show you. Then, together with a thinggy and then another whatsit you assembled this 'Gauge, testing something or other' and screwed it to the threaded mortar body. You wonder who invented it. I presumed that it was the same man who dreamed up time and motion on the battlefield. Anyway....... We all practiced hard with this gadget and took it all seriously - as you do. It took ages to get a result because each mortar had to be done three times and then a mean average had to be worked out and........... and........

That was fine, until we took all of this newly learned knowledge to our first units. Mine was a front line Infantry demonstration battalion at the School of Infantry where we were knee deep in 2" mortars. That's when I realised that our special gadget for testing 2" mortar was rusting away, unloved and unused in the back of an old cupboard. That was when Johnny Sparrow taught me the way things were in real lofe, at the sharp end. He pointed out to a red line painted line on the wall, about 6 feet off the ground (and to one side of the florescent strip light I hasted to add.....). He then told me that to test OUR mortars - and the way that they were tested everywhere else in the known universe, - was by putting an old copper penny piece into the firing ring and pulling the landyard/firing lever. The spinning coin spun upwards and if it passed the red line, all was well. If not, you did it again until it DID spin past the red line.

So simple............
There was a little humourous sequel to this if anyone wants a laugh......

[Surpmil]

Don't know, but I saw a 1944 manual on the proofing of SA ammo on a library shelf recently and am going to photograph the whole thing.

Badger can maybe find a home for it here somewhere?