doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Help needed on pressures of modern loads?

Jack, SAAMI maximum average working pressure for 12 gauge is 11,500 psi (as stated above).

A proof pressure for SAAMI loads of 1.5 x working is between 17,000 - 18,000 psi, hence proof loads of ~ 18,000 psi, as you surmised. This is also essentially equal to the 1,200 kg/sq cm "heavy" proof used optionally in Spain and similar levels available in France and other countries.

I think it's reasonable to view the 3 Ton/650 bar/10,730 psi pressure as the maximum service/using pressure rather than the standard/recomended service pressure. The Gamebore loads run below 8500 psi but are 'approved' for use in 3 ton/650 bar service/850 bar proof guns.

Miller, I'm a writer. I do this stuff for a living. A review of my previous post--the one you quoted--shows no references at all to anything about guns marked with "tons". However, the paragraph preceding the one you quoted does, in fact, refer specifically to guns with the bars proofmarks. But just to make clear, the only thing I'm certain of is that the 10,730 and 13,920 psi figures are the transducer equivalents for service pressure and proof pressure, respectively, of guns proofed under the CURRENT system.

Thus, you may have INFERRED something from my post, but it was nothing that I IMPLIED. I made that clear in my most recent post, when I said that I would contact the Birmingham Proof House to clarify proof and service pressures for guns from the "tons" and earlier eras. I have done so; currently awaiting a reply.

Ok, 1st, I am not going to even touch the CIP/BAR/TON/PSI/PIEZO/CRUSHER discussion...the relationship is a curve so a simple linear expression will not be accurate in all instances.

Recoil and pressure are related. However, the relationship is complex. The calculation to arrive at chamber pressure includes many more variables. Perhaps a definition of pressure is needed. From the SAAMI website:



So you press the trigger and a lot of energy is released. Where is going? Up the barrel? Well only to a degree, few things are 100% efficient.



As you can see, one event causes multiple responses. Gun powder is burnt. Gases are released. The load begins to move. The barrel starts to flex in 3 dimensions. Heat is generated.

Part of this is measured in recoil. A simple law of Newtonian physics, "For every action there is a reaction". But something more complex is occurring. In part the burn rate of the powder, not just how many grains you used, plays a role in determining pressure. Think of it this way. If you are lighting a BBQ and all you have is some paper, the flame takes a while to get going. Soak a little starter fluid on the paper and it burns at a very different rate. With gun powder the size, shape and detergent coatings play a role in determining the burn rate. Did you ever look a burn rate chart? They are very informative:
http://www.reloadbench.com/burn.html
http://www.reloadersnest.com/burnrates.asp

Ammunition manufacturers use very precise calculations to determine the loads they develop. Then they do a lot of pressure tests and chronographing of the projectile. They walk a thin line. Their goal is to produce a load with a certain muzzle velocity while keeping the pressure within SAAMI standards.

They are dealing with a working pressure that has been established, requiring that the powder burning rate (relative quickness) be matched to load acceleration to produce optimum velocity. For a given pressure the optimum velocity can only be obtained by maintaining the accelerating force for a longer or shorter period of time.

To think that the British companies have a different objective than American, than Italian, than German is not true. They are all relying on the same buyer. What is true is a relatively small percentage of shooters choose to shot a 100 year old gun with 2 barrels that was proofed using methods no longer in use. Most prefer a semi-automatic and Wally World Wonder Shells.

Pete

Just heard back from B&P regarding their speed/pressure chart:

"The B&P Pressure chart has nothing to do with SAAMI. Those are the actual PSI( pounds per square inch ) for the actual Baschieri & Pellagri loadings that we import into the United States."

Looks like their psi is CIP/LUP (which explains why their bar to psi conversions fit the formula) and we need to add 1000 for a rough approximation of SAAMI pressure.

From a separate post it sounds like RST will tell folks the PSI for various loads they offer.

I had no problem getting the pressure infro from RST, Polywad, Fiocchi, Kent, Gamebore, or the Bismuth folks. Federal responded but was vague "It generally runs between 9000-10,500 psi" Remington, Eley, and Winchester never responded to my requests, and I intend to purchase shells from those that did.

"Those are the actual PSI( pounds per square inch )"
Note that if these are LUP pressures then they "Are Not" actual psi. We poor peons will never sort all this out until the makers & proof houses decide to use correct terminology. 1 actual psi should be 1 psi whether measured by SAAMI, CIP or whoever. Some 40 yrs ago we of the US quit using the psi term except on those pressure recorded by the tranducer method which repotedly gives correct readings. Others are listed as LUP's or CUP's depending upon the crusher metal. The 14.503 conversion factor between psi & bar is based upon "Actual Correct" pressure readings, not crusher pressure.

Precisely! What B&P is doing--quite easy to see, from their charts--is a straight conversion from bars to psi. What we know, from the Birmingham Proof House, is that the bar readings are not always transducer measurements. If they're crusher measurements, then the formula does not yield the answer in REAL psi. That's why our reloading manuals specify pressures in either psi or, occasionally, in LUP. If it's in LUP, then we know that figure was arrived at under the crusher rather than the transducer system, and about the best we can do is a "ballpark" conversion to psi by adding 1,000. Build in something of a fudge factor to be on the safe side and that's good enough for reloading purposes. But as we've seen from the Brits, if we assume crusher bars to be transducer bars and attempt to do the math, we're going come up with a psi total that's quite a ways off--although at least it's off on the safe side.

Still awaiting a reply from the Birmingham Proof House. I'll post it as soon as I hear. I think all of us that play with older Brit guns would like to have some more definitive answers.

I thought these might be interesting to see. From a recently acquired book...

1895 Crusher jig - Liege


circa 1900 multiple crusher test setup - Liege


Various powder testers - Liege


Pete