doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com 3 inch CIP v 3 inch SAAMI pressures

Just fiddling through the CIP Homologation pages I came across these shotshell pressure tables:

CIP Shotshell Pressures

This indicates that the max service pressure for 3 inch CIP shells is 1050 bar = 15229 PSI and the proof pressure is 19245 PSI.

SAAMI service pressures are 11500 PSI across all 12 gauge cartridges except the 3 1/2 inch cartridges. I believe SAAMI proof pressures are in the 20000 PSI range.

That is some difference between the two Max service pressures.

I have probably read the figures all wrong but in case I haven't then my questions are:

1. Are CIP 3 inch cartridges usable and safe in US made 3 inch chambered guns? (given that the proof pressures are similar they should be).

2. Have CIP superior proof pressures changed from the original British Proof house nitro proof pressures for 3 inch 12 ga. cartridges ( as in "back in Greener's day!)? (The standard proof apparently has not).

3. Given that max pressures for SAAMI specs 3 inch cartridges are only 1000 or so PSI more than the standard CIP proof at 740 bar = 10730 PSI are they safe to be shot in three inch chambered British guns with the older 1 1/2 oz = 3 1/2 tons per square inch proofs. These are built much stouter than the typical English game gun and obviously proofed for higher pressures.This does assume all guns are in proof.

4. Does anyone know what the proof pressures were for the 1 1/2 oz = 3 1/2 ton per sq. inch proof pressure was?

There is a blackpowder proof charge for 3 inch nitro proof given in Greener's book. I have no way of measuring the pressure generated nor even of getting blackpowder. Has anyone ever tried this charge for pressure?

Thanks for any and all observations and corrections.

All the best

Skeeterbd

I own a 1906 Purdey That was sleeved, presumably by Purdey or Teague for Purdey, so that the owner then could use British 3 inch shells for waterfowl. The bbls show all the proper proofmarks.

Would American 3 inchers be safe ?

danc

Skeeter, the 740 bar pressure you mention as proof pressure is in fact the service pressure for 12 gauge guns of less than 76mm chamber, ie non magnums.

If the chamber is 76mm then the gun must be submitted for compulsory proof at 1370 bar. The same standard is vountary for 70mm chambered guns. The compulsory proof for standard chambers is 960 bar.

This leads to some confusion in Europe because there are 70mm shells generating 1050 magnum service pressures, but these are marked on each shell (thankfully!), not just the box. To add to the confusion Proof Houses do not have a clear numerical indication of pressure, most having a stamp which the public are expected to interpret.

Proof pressure have changed over the years, the latest changes came about in the early 1990s when magnum proof pressure increased from 1200 to 1370 bar and regular proof from 900 to 960 bar.

You can get the CIP table showing proof and service pressures for each gauge from the CIP site.

Crowley, what do these "proper" proof marks say?

The rule of thumb for us in Europe is that guns are proofed at service pressure plus 30 per cent. Therefore service pressure is proof pressure minus 25 per cent. And bear in mind the British and Russian practice of stamping service pressure on their guns, not proof pressure as the rest do. So on a British gun the stamp 3 1/4 tons, or in a Russian gun the 750mpa are the service pressures, not the proof pressures. On all others the pressue indicated on the gun is the proof pressure and must be reduced by 25 per cent to figure the service pressure.

Proof pressure is the actual pressure the gun withstood during testing. Service pressure is the pressure it is meant to withstand in regular use.

Keeping it simple tends to keep it safe too.

Shotgunlover

Thanks for you kind observations.

I have looked at the list of CIP proof pressures. I do know that the 740 bars is the service pressure for standard proof guns. I obviously did not state it in my post correctly.

If proof pressures have changed from 1200 bars to 1370 bars then was the older 1200 bars the equivalent of the old 3 inch proof of 3 1/2 tons per square inch? (To further add a twist: was the 1200 bar pressure measured by transducers or was it LUP?)

1200 bar (transducer) should lead to a 900 bar service pressure (13050 PSI)

My real question was that are American three inch shells at 11500 PSI service pressure safe in older (in proof) 3 inch chambered British guns?

The standard proof service pressure is 10730 PSI. The maximum allowable pressure in individual loads is 850 bar as per the CIP tables(while maintaining a max average pressure of 740 bar).

850 bar is 12328 PSI. So the odd 11500 PSI cartridge of appropriate length in the appropriate chamber ( i.e. 2 3/4 inch shell in 2 3/4 inch chamber) will be handled with ease even by standard proof guns.

So by that "logic" the much heavier proof and stouter build of even older 3" chambered ( 3 1/2 tons per square inch service pressure) British guns should allow them to easily handle American 3 inch shells at 11500 PSI (792 bar, say 800 bar)!

As always ready to be shot down in flames.

Thanks again for your interest and clarification.

All the best

Skeeterbd

Some confusion here--no surprise at all!--concerning CIP proof. The CIP "change" in proof pressures in the early 90's was, in fact, only a change in the way pressure is measured, not the pressure itself. 850 bar standard/1200 bar superior or magnum continued to be stamped on British guns until 2006, at which point the bar figures were dropped entirely and replaced by STD under one crown for standard, SUP under 2 crowns for superior. What happened in the early 90's is that the CIP countries, which had been using the old crusher system of measuring pressure, switched to the modern electronic transducer system. Transducers--which SAAMI had been using for quite some time before CIP countries converted--give different pressure readings than crushers for the same shells. The old crusher readings, in SAAMI terminology, are expressed as LUP (lead units of pressure), which you'll see in some reloading manuals. Transducer readings are psi.

So CIP didn't really increase proof or service pressure standards. All they did was express it in numbers derived from transducers rather than crushers. And the transducer numbers are higher (just as psi values are higher than LUP), which makes it look as if pressures were increased. To further add to the confusion, the Spanish proofhouse started marking their guns with the new transducer numbers, while the British proofhouses continued to use the old crusher numbers for their proofmarks--even though both countries converted to the transducer system in the early 90's.

No wonder there's confusion on this subject!

Note also that in perusing many "Old" US reloading manuals pressures will be given in PSI which were truly LUP's.
The old British 3� Ton pressure was service pressure taken by the crusher method. It translates to approximately 10,640 PSI, so about 1,000 PSI lower than 3" SAAMI pressures.

I have a Lyman reloading manual from 1984 that expresses all pressure values in LUP, and in the section on pressure, describes in detail the crusher method of measurement. The information I have from SAAMI includes a data sheet from 1984, which refers to the crusher method as "the older method of pressure measurement". And the current SAAMI pressure tables date from 1992 (all psi). I'm not entirely clear on when we started using transducers here in the States, but it would appear that there was a transition period. Much like the conversion from the old short chambers to 2 3/4" in the years before WWII, it didn't happen all at once.

Thanks for the replies L Brown and 2 piper.2 piper:

From what I understand, if 3 tons per sq. inch is equal to 740 bars (transducer) which is 10730 PSI then 3 1/2 tons per sq. inch must be greater than 10640 PSI (transducer). I believe that crusher pressures don't translate directly to transducer PSI and give much lower than true figures if the usual conversion formulae are used.

See L Brown above, viz: "So CIP didn't really increase proof or service pressure standards. All they did was express it in numbers derived from transducers rather than crushers. And the transducer numbers are higher (just as psi values are higher than LUP), which makes it look as if pressures were increased"

I am as usual probably wrong.

All the best

Skeeterbd

Skeeterbd;
I am not so certain that 3 tons & 740 Bar are equal. back while the Tons system was still in use Burrard reported that simultaneous pressure tests had been run using both lead crushers & Piezo Electric transducers & a fromua worked out which within the range of shotgun pressures "Only" would be very close. Close enough in fact to avoid trouble from its use. The formula was Crusher Tons times 1� minus 1/2 ton = Transducer Tons. Thus 3 x 1.5 = 4.5; 4.5 - .5 = 4. As the Ton here is the 2240 lb long ton then 4 x 2240 = 8,960 PSI. Using the same formula 3� Tons = 9,800 PSI, 3� tons =10,640 & 4 tons = 12,320 PSI.
From what knowledge I have of the subject these do indeed seem to be very close conversions. It is of course true that crusher pressures do not translate directly to transducer PSI. "IF" they did then 3 Tons would =6,720 PSSI & 3� Tons would = 7,840. It is also obvious that the act of adding 1,000 lbs to the crusher reading is not going to be close either. Both of these are more than 2,000 lbs off the crusher reading.