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eeb #613455 04/04/22 08:56 AM
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What Bro. Larry said

High Performance "Superior" (Magnum) MSIP is 1200 BAR = 17,405 PSI for a Service Pressure of 1050 BAR = 15,229 PSI, and Mean Proof Pressure of 1320 BAR = 19,145 PSI.

BTW: FABARM voluntarily proof tests to 1630 BAR = 23,641 psi

eeb #613459 04/04/22 01:56 PM
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vatt essen dare formuler, converten dare bars unt tu dare psen unt dare i's...


advocating doublegon happiness...via 90/30 guidelines...
eeb #613469 04/04/22 10:29 PM
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https://bobp.cip-bobp.org/en/tdcc_public?page=1&cartridge_type_id=7

This is the CIP pressure guides for all CIP proof shotguns now. From it you can see the proof level of 850 and the PT max service level of 740 bars. This is just an updated value in bars, instead of tons per square inch.

Formula: multiply the value in bars by the conversion factor '14.503773800676'.

740 bars is 10,732.79 psi. That is the service pressure often discussed. So if your gun has a service pressure of 10,700psi shooting shells in the 7-8,000 is a very conservative safety decision.

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Originally Posted by KY Jon
Pressure can be calculated by a formula. P is pressure, F is force and A is area. Pressure equal the force divided by the area.

P=F/A

Pressure seems simple to understand as it is the result. Measure the force and calculate the area. Force is the effect of the gasses and shot acting against the barrel wall, the empty shell, the breach behind the shot and air in front of the shot, Area is the volume of space as the gases push the payload down the barrel. So as the shot goes down the barrel, the area increases and this is why we can shoot barrels not as thick as the chamber area, where the volume is smallest and the pressure can be the greatest.This is also why a slow burning powder can have lower pressure early but still achieve a good velocity. They also can have higher pressure down the barrel, compared to a faster burning powder which may peak early and drop off quicker. There are a ton of variables such as how fast a powder burn rate, how hot a primer to achieve quick ignition and full burn of powder, compress-ability of shot, steel compresses less than lead and the amount of compress-ability of the wad which will spread the pressure out a bit by absorbing energy as it collapses. .


Um, no. There is an awful lot wrong with this statement. First off, Area and Volume are two entirely different things. That definition of Force is also incorrect. And nobody is going to be able to calculate the peak chamber pressure or show the pressure curve of a given shotgun shell load by applying this P=F/A formula either. That's why we have to rely upon pressure data from either the ammunition factory, or employ the services of someone like Tom Armbrust, who has the equipment to accurately test shotgun shells. They do not use a calculation to determine pressure. Modern ballistics labs use piezo-electric transducers to read pressure in the chamber and along the length of the barrels. Older pressure guns had a piston that compressed a lead or copper crusher The amount of compression was measured with a micrometer and the amount of compression was converted to lead units of pressure (LUP) or copper units of pressure (CUP), and only told us peak pressure. Here is a pretty good general explanation of old and new methods of cartridge pressure testing:

https://www.shootingtimes.com/editorial/ammunition_st_cuppsireloaddata_200905/100105

And in less time than it took Ed to post this nonsense, he could have simply Googled "convert bar to psi".

Originally Posted by ed good
vatt essen dare formuler, converten dare bars unt tu dare psen unt dare i's...


A true sign of mental illness is any gun owner who would vote for an Anti-Gunner like Joe Biden.

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740 bars is 10,732.79 psi. That is the service pressure often discussed. So if your gun has a service pressure of 10,700psi shooting shells in the 7-8,000 is a very conservative safety decision.[/quote]

Bullseye! That margin of safety even covers some (relatively moderate) increase in pressure from firing a 2 3/4" shell in a 2 1/2" chamber.

eeb #613481 04/05/22 09:51 AM
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Maybe we ought to make this thread, or one like, it a sticky. One of the most asked and often misunderstood question, is what load to shoot in my gun? A gun in proof, which has been inspected by a knowledgeable gunsmith, should be safe shooting a “service pressure” load of 740 bars which is 10,732.79 psi. For additional margin of safety you can always go lower, as I do. A Black Powder proofed gun gets loads comparable to what was original to it, and those are 4,500-5,500psi. Or if you can load them, real black powder loads which always draws a lot of attention.

Drew has posted a lot of very detailed information on this subject, along with pressures for period loads for the 1890-1900 timeframe. Look at his website to see real numbers. Look at the CIP link I posted, for real numbers. I posted the formula to calculate bars to psi. Go to Hodgdon or Alliant to find real pressure numbers for any reloads. Any factory CIP approved load will be at or below Service pressure. But the bottom line is normal service pressure is 10,732.79 psi. That goes for 2 1/2”, 2 3/4” or 3” if proofed at 850 bars. I also think 2” are now proofed at the same but check it on the CIP to be certain.

We know shooting 2 3/4” shells in 2 1/2” chambers does increase pressure some. Most reports have bee 1,000psi or less. You decide what to do about that. I cut hulls down to 2 1/2” but if the pressure was 5-7,000, in a 10,000 gun, that is over caution. I still do it.

Last edited by KY Jon; 04/05/22 10:07 AM.
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eeb #613523 04/06/22 06:36 AM
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I just thought for completes I would photograph a couple of cartridge box tops containing information about the contents inside. The top box flap is Hull cartridge company this being my go to for all my nitro proof 2 1/2 chamber guns the other is if I want something a little faster the Lyalvale for clay though still for all my 2 1/2 chamber guns. There is no pressure quoted because here we only need to know the gauge chamber length and shot weight, so if your gun is in good condition and in proof for the type of propellant in this case Nitro the cartridge can be used in any gun irrespective of age in my case gun's made from 1860 to 1950 all my other guns are 2 3/4 chambers.

[Linked Image from i.imgur.com]


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Originally Posted by KY Jon
Maybe we ought to make this thread, or one like, it a sticky. One of the most asked and often misunderstood question, is what load to shoot in my gun? A gun in proof, which has been inspected by a knowledgeable gunsmith, should be safe shooting a “service pressure” load of 740 bars which is 10,732.79 psi. For additional margin of safety you can always go lower, as I do. A Black Powder proofed gun gets loads comparable to what was original to it, and those are 4,500-5,500psi. Or if you can load them, real black powder loads which always draws a lot of attention.

.

Jon, there's an issue with the bars figures you use. Back when the Brits stamped their guns 850s bar proof, the service pressure figure they used was 650 bars service pressure. BOTH of those figures were derived by the old lead crusher system. You correctly converted 650 bars crusher to 740 bars transducer so that it could then be converted to psi using the mathematical formula. 850 bar is also a crusher-derived figure. Thus, it also needs to be converted. The proof pressure for an 850 bar gun is 960 bars transducer, which converts to 13,920 psi proof pressure. That's straight from Roger Hancox, the former Birmingham proof master. But as you point out, the 10,730 psi service pressure is the number that's really important as we work up reloads for guns marked 850 bar, or the current "STD".

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eeb #613530 04/06/22 08:41 AM
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Interesting and thank you damascus.
When did British shell box discontinue?

These cartridges are suitable for use in:
70mm case length: Guns with a chamber length of 2 3/4” or longer, nitro proofed to a service pressure of 3 1/4 tons per square inch (900 kg per square cm)
67 mm case length: Guns with a chamber length of 2 1/2” or longer, nitro proofed to a service pressure of 3 tons per square inch (850 kg per square cm)

eeb #613537 04/06/22 09:55 AM
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Yes Larry, you are exactly correct. I am trying to keep it as simple as possible and as you pointed out the bottom line is what is “service pressure” and what that means for safe pressure loads to shoot. 10,733.79 is the service pressure but most UK ammo I’ve seen is far under that pressure. They just don’t seem to have the mania for hot loads we have. Why I don’t think they even think every hunting load ought to be going 1450fps, that seems to be the norm today. I am sure far more birds have been killed with loads below Service Pressure than above for the simple reason most loads always fell under it until modern powders started generating our current much higher pressures.

All we need is a simple rule of thumb type guidelines. If proofed at 850 bars keep pressure below 10,700psi. Or just under 10,000 for round numbers. To be kind to your stock aim for 7-8000psi, 1150-1200 fps. With 1 to 1 1/8 ounce shot. Since the stock suffers from recoil, not chamber pressure, and recoil is directly related to force, (velocity & payload), keeping both down reduces stress on wood. But “safe” is safe for the barrels, the rest is about wood health.

It would be nice if the UK did not have about half a dozen ways of saying the same basic thing and three, now four levels of proof information. But we are talking about a period of 150 years and things have changed a lot. black to nitro, Drams to tons to bars, chambers thrown into the mix with shot charge for good measure and now Superior Steel proof. Can’t see why anyone would get confused.

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