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Posted By: eeb UK Proof Question - 04/03/22 12:43 AM
I’m looking at a high condition 10 gauge boxlock with twist barrels. It was reproofed in 1989 with 70mm chambers, 11/2 oz shot at 850 bar. By virtue of the heavier shot charge I would think working pressure would be greater than 850 bar. Am I incorrect?
Posted By: Ted Schefelbein Re: UK Proof Question - 04/03/22 12:54 AM
I don’t think so. 850BAR is about 12,090, working pressure perhaps 10,750. Working pressure runs less than proof pressure. Not sure a guy should run old twist barrels up anywhere near proof load pressures.

Best,
Ted
Posted By: eeb Re: UK Proof Question - 04/03/22 01:25 AM
You are correct. I mixed up proof and working pressures. Still, 850 bar is proof for 1 1/8 oz, 1 1/4 oz and 1 1/2 oz. It seems all that matters is case length since all those loads are proofed at the same pressure.
Posted By: KY Jon Re: UK Proof Question - 04/03/22 01:41 PM
That 1 1/2 oz. is not traveling as fast as that 1 1/8 oz., load as a general rule. It is possible, but most loads travel faster for a lighter load and slower for a heavier load. That keeps the pressure more equal when you lack today's slower burning powders. That is the beauty of the proof system. Any gun under proof, is approved for any shell loaded to that proof service level. "Standard" CIP proof is 850 bar and has been that way since 1979. Standard proof working pressure, is up to 740 BAR (10,733 PSI). All, myself included, have been obsessing about here is what "standard CIP proof" has been for decades: standard proof "working pressure" is up to 740 BAR (10,733 PSI). No, you cannot shoot "right up to proof pressure", and is exactly why the CIP publishes "working pressure" load limits. We are making it just too hard. If your 12 gauge gun has 850 bar proof, at any shot load, which is no longer stamped on the gun anyways, then you working service pressure ought to be 740 bars, which when calculated should be about 10,733psi. If your load is under 10,733psi you are good, even better for the old stock if less, because old wood gets fragile.



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.

So what does this all mean. Well nothing and everything. The length of the shell is no more a certain predictor of pressure, than the length of the brass on the case. UK used long shells, pushing the same shot load used, more and better wadding. It is true there is more room for heavier load, the final limit is service pressure which being kept equal would tend to push heavier loads slower than light loads. Pigeon guns often had long chambers but the shot load was restricted by rules so the incentive was to get more and better wadding, not to cram in more shot. Speed does kill but better patterns kills as well and Black powder loads most likely were velocity limited by Black burn rate.

Now with modern powders, you can get higher velocity, with lower peak pressure because the burn rate is slower, so the area is increasing as the load goes down the barrel. That is the case until the burn rate is too slow and you get incomplete total burn of the powder and shells which vary in results form one to the other. That is why you struggle to get Longshot light loads to go much under 1250fps. If you drop the charge too much it gives you bloopers.
Posted By: Drew Hause Re: UK Proof Question - 04/03/22 02:26 PM
The G.E. Lewis "Magnum" 3" with 1 1/2 oz. shot 12b were introduced c. 1920 (before Olin's Progressive Burning Oval)

[Linked Image from photos.smugmug.com]

Major Sir Gerald Burrard, The Modern Shotgun, Volume II, “The Cartridge”, 1955 3rd Revised Edition reported pressures (converted from Long Tons/ Sq. Inch)
10g 2 7/8” 1 7/16 oz. 4 Dr. Eq. standard service 9,296 psi with maximum service 11,984 psi
12g 3” 1 1/2 oz. 3.57 Dr. Eq. standard service 9,632 psi with maximum service 12,320 psi
Posted By: lagopus Re: UK Proof Question - 04/03/22 02:27 PM
According to my copy of the 1989 Rules of Proof book. For Standard Proof 4 & 8 bores are Proofed at 800 bars. 10, 12 &14 bores at 850 bars, 16 bores at 900 bars and 20, 24, 28, 32 and .410 bore are proofed at 950 bars. The larger the bore the less the pressure as the gas has more room to play in and the tighter the bore the greater the pressure; a bit like squeezing a hose pipe and getting to blow off where it fits the tap. Lagopus.....
Posted By: eeb Re: UK Proof Question - 04/03/22 04:53 PM
Thank you gentlemen for your responses
Posted By: Drew Hause Re: UK Proof Question - 04/03/22 06:29 PM
This is an updated version of the CIP regulations converting BAR to PSI using piezo transducer derived numbers

12g 50mm, 65mm, and 70mm “Standard Proof” lead or steel Maximum Average (SERVICE) Pressure 740 BAR = 10,733 psi; Maximum Statistical Individual Pressure 850 BAR = 12,328 psi; Mean PROOF Pressure 930 BAR = 13,489 psi

Both 65 and 70 mm 16g standard is SERVICE 780 BAR or 11,313 psi; Maximum Statistical Individual Pressure 900 BAR or 13,053 psi; PROOF 980 BAR or 14,214 psi.

Both 65 and 70 mm 20g standard is SERVICE 830 BAR or 12,038 psi; MSIP 950 BAR or 13,779 psi; PROOF 1040 BAR or 15,084 psi.
Posted By: KY Jon Re: UK Proof Question - 04/04/22 01:52 AM
Like I said, we make way too much about service vs. proof pressure. As a personal choice I go for lower than service pressure levels in my loads. I can easily find 12 loads in the 5,500 to 7,000psi which handle almost all my shooting needs. For the 20 I bump it up to 8,000 to 8,500psi but do not get excited about 9,000psi. If you reload that gives you a ton of loads to draw from even in these times of difficult to find powders. Factory pressures for American shells are loaded to SAAMI safe levels which are higher. Unless I know for certain what they factory pressures are I just go with my re-loads or CIP approved ammo. Every shell I have loaded on my shelves are low pressure loads, with the exception of a few small batches of loads for hunting situations and they are clearly marked on the primer end. You might need to check if it is 2 1/2 or 2 3/4" at most and my pressures are so low that is not even that big of a deal. I have been much more relaxed about "service pressures" ammo for my classic doubles since I went to uniform loads. The shot size may change depending on intended use, but a 1150fps, load low pressure load, is safe in any gun I own and shoot. About as simple as it can get. I can go down to 1100fps and a few go 1200 but nothing so silly as the current rage of 1450fps ammo which seems to be the current default shell everyone seems to use.
Posted By: L. Brown Re: UK Proof Question - 04/04/22 10:48 AM
Originally Posted by Drew Hause
This is an updated version of the CIP regulations converting BAR to PSI using piezo transducer derived numbers

12g 50mm, 65mm, and 70mm “Standard Proof” lead or steel Maximum Average (SERVICE) Pressure 740 BAR = 10,733 psi; Maximum Statistical Individual Pressure 850 BAR = 12,328 psi; Mean PROOF Pressure 930 BAR = 13,489 psi

Both 65 and 70 mm 16g standard is SERVICE 780 BAR or 11,313 psi; Maximum Statistical Individual Pressure 900 BAR or 13,053 psi; PROOF 980 BAR or 14,214 psi.

Both 65 and 70 mm 20g standard is SERVICE 830 BAR or 12,038 psi; MSIP 950 BAR or 13,779 psi; PROOF 1040 BAR or 15,084 psi.

Very good info, Doc Drew.

Of course neither the proof nor service pressure figures are currently stamped on British shotguns. They've been replaced by STD for standard proof and SUP for superior or magnum proof.
Posted By: Drew Hause Re: UK Proof Question - 04/04/22 12:56 PM
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
Posted By: ed good Re: UK Proof Question - 04/04/22 05:56 PM
vatt essen dare formuler, converten dare bars unt tu dare psen unt dare i's...
Posted By: KY Jon Re: UK Proof Question - 04/05/22 02:29 AM
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.
Posted By: keith Re: UK Proof Question - 04/05/22 10:48 AM
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...
Posted By: L. Brown Re: UK Proof Question - 04/05/22 10:59 AM
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.
Posted By: KY Jon Re: UK Proof Question - 04/05/22 01:51 PM
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.
Posted By: damascus Re: UK Proof Question - 04/06/22 10:36 AM
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]
Posted By: L. Brown Re: UK Proof Question - 04/06/22 12:09 PM
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".
Posted By: Drew Hause Re: UK Proof Question - 04/06/22 12:41 PM
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)
Posted By: KY Jon Re: UK Proof Question - 04/06/22 01:55 PM
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.
Posted By: L. Brown Re: UK Proof Question - 04/11/22 11:19 AM
Originally Posted by KY Jon
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.

Jon, sometimes I think that our cousins across the Pond do it just to confuse us! The shotshell box is yet another example. They don't express velocity the way we do. Ours is quite consistent: it's measured at 3 feet from the muzzle. Theirs may be either a)"True" velocity, measured at the muzzle; or b)"Observed" velocity, which is the average over 20 yards; or, most recently, c)"Mean"velocity, taken at 2.5 meters from the muzzle. True velocity would lead Americans to believe that British shotshells are faster than American shells. Observed velocity, which is 1070 fps for a "standard" load, would lead us to believe that their shells are a good bit slower than ours. I'm guessing the Lyalvale shotshell box above carries a true velocity reading. The observed velocity standard for a high velocity load is 1120 fps. That equates to an American load with a listed velocity of 1235 fps. 1400 fps must be a reading taken at the muzzle.
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