doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Proffed for 3 tons ???

I spent some time this morning trying not to bring up again but never found anything expaining 3 tons pressure or 850 bar. None of the books that I have explain it either.
Where do I find it?

This post might be a good place to start:
Conversion Tables, Proof, and Pressure Information

I couldn't bring up the thread on the 16g site, and some here so enjoy cut and paste drivel I thought I'd post it with apologies.
Bro. Larry did all the work.

The "Tons" mark (which is service pressure) was not used until 1954. Between 1925-54, only the chamber length was marked. 1904-1925 guns would only have the shot charge and 'Nitro Proof'.

There are three pressure measurement systems (lead crushers/LUP, copper crushers, and piezo), and two standard systems of measure units (USA/SAAMI and CIP/British/European) and different units within each system (psi, tons/sq inch, and bar in kg/cm sq).

There is essential NO formula to convert BAR expressed as LUP (CIP) to PSI (SAAMI). LUP + 1000 does not reliably predict the actual piezoelectric transducer measured pressure.

Starting in 1989, all CIP proof data was marked in metric using BAR as the unit of measurement. The use of TONS per square inch was dropped. Under this system, 850 bar represented standard proof, with 1200 bar being special or magnum.
2 1/2" chambered guns are usually proofed 850 bar.
2 3/4" chambered may be proofed 900 bar or higher.

Per the 1954 Rules of Proof, here are the approximate CIP service pressure values:
3 tons--8,938 psi
3 1/4 tons--9,682 psi
3 1/2 tons--10,427 psi
4 tons--11,917 psi
These numbers SHOULD apply to guns proved under the 1925 rules; a 2 1/2" chambered gun proof would be equivalent to 3 tons; a 2 3/4" chambered gun to 3 1/4 tons.

European (CIP) proof pressure of 850 kg per sq. cm. (BAR) = about 13,920 psi proof pressure = about 10,730 psi service pressure (SAAMI)

Per the 1954 Rules of Proof, here are the approximate CIP service pressure values:
3 tons--8,938 psi
3 1/4 tons--9,682 psi
3 1/2 tons--10,427 psi
4 tons--11,917 psi
These numbers SHOULD apply to guns proved under the 1925 rules; a 2 1/2" chambered gun proof would be equivalent to 3 tons; a 2 3/4" chambered gun to 3 1/4 tons.



A Brit Long Ton/sq in = 2240 psi (rounded off,,afaik).
3 Tons would be 6720 psi.
Where does the '8938 psi' number fit in.

Is one the service load pressure, the other the proof pressure? Or am I looking at this all wrong and have an incorrect conversion factor to begin with. Wouldn't the first time for that!

Certainly no math wizard here. Just wanting to understand.
Thanks.

I've always wondered about the 3 tons/850 bars thing. During the late 80's, both those marks were still being used by the proofhouse, but I THINK (although am not positive) that the proof pressure was the same. And I know that the 10,730 psi service pressure figure (piezo) for 850 bar guns is correct. That one is straight from the Birmingham Proof House. Which causes me to wonder whether the 8900 psi service pressure figure for the 3 ton guns might not be a crusher number rather than piezo. Using the LUP = 1,000 = psi, which is only a ballpark guesstimate, 8900 sounds too low. But I don't believe they changed the proof and service pressure standards when they went from the old tons system to the new bars --although again, I may be wrong.

This conversion is still an estimate because of the difference in the technique. To convert the Lead Crusher Pressure (Cp) to PSI (pound force per square inch)

(Cp x 1.5) - .5 = TSI, TSI X 2240 = PSI

3 Tons per Square Inch (UK, Long)

3 x 1.5 = 4.5, 4.5 - .5 = 4 TSI, 4 x 2240 = 8960psi

Thank you
It may be boring for you but I spent some time this morning and could not find a trace of a chart. Even at the Birimgham Proff house. I am shooting 2 1/2 dram eq 7/8 oz reo shells at 1200 fps in a sleeved Island lock Purdey proofed at 3 tons. I have not spent any time trying to find out if this is too hot for the gun but I wonder if they are on the edge of hot or not?

B&P lists their 12g Legend 24 gram (about 7/8 oz.) at 1230 fps as only 450 BAR calculated (not measured) to be 6530 psi. Rio should be similar.
I use their Competition One 7/8 oz at 1160 which is 5,804 psi with very light recoil.
http://aerostaroutdoors.com/catalog/index.php?cPath=1_24_55 is currently out of stock

http://www.bandpusa.com/content/Speed-and-Pressure-Chart.pdf

Thank you for the explanation. I'll have to think that one thru.

I still can't get past the point that if TSI X 2240 = PSI
1 TSI would = 2240 psi
3 TSI would = 6720 psi

If the Lead Crusher conversion formula to PSI gives 8938 psi for a '3 Ton' reading, that would seem to be an awfully wide difference from the straight 2240psi/Ton x 3 method.

I'm hopeless,,,and have been told so many times.

I'll keep studying it.
Thank you for taking the time. Always interesting.

Kutter;
The lead crusher did not give actual PSI, even though in its day it was often stated as such. The more correct label is LUP's (Lead Units of Pressure). 3 long tons tons is 6720 lbs. The formula which Drew cited is one which was done by the British when they began using the Piezo Electric (PE) method & was derived by taking pressure by "Both" methods simultaneously. It was never stated to be an exact formula but "Close Enough" for pressures within the normal range of a shot gun. It is as far as I know applicable only to pressures listed in British tons. As noted running the formula for three tons came within 22 lbs of that cited by the proof house, while the mere expedient of adding 1,000 lbs still misses the mark by more than 1,200 lbs, not even in the same Ball Park. When lead crushers were being used they were calibrated by what was essentially a static pressure, but in taking the pressures from the barrel the pressure was on them for so short a time they simply did not reach full compression, thus LUP's always read less than actual PSI. The PE gauges read virtually instantaneous & give true PSI readings.