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Chicago Offline OP
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After seeing post on burst barrel I checked the proof marks on my 12 ga - just to be sure so to speak. It has 2 1/2" chambers and according to proof marks is for 1 1/8 oz and 850 bar. This gun was probably manufactured in England sometime around 1900 - 1910. Wall thickness is at least .034 in both barrels.

Does anyone know what PSI 850 bar equates to? I know I saw a post about pressures for different manufacturers for 16 ga recently. A few showed both PSI and BAR. Has anyone seen, or know where I can find similar information for 20 and 12's.

To date I have always used either B&P's or Gamebore's Pure Golds in gun less than or equal to 30g. I think that equates to about 1 1/8 oz or less. My limited understanding is that these loads should be ok. Howevever, nothing on box or web sites reflects actual pressure.

Thanks in advance - I am fond of all my appendages.

Chicago (Mike)

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A while back I paid a few bucks to the 16ga reloading group for their spreadsheet of load data. When I did so I agreed not to publish the data, so I won't post it here--if anyone wants it, I suggest emailing russel Gray and joining up--it's well worth the money. Also keep in mind I'm no expert, I'm merely regurgitating my interpretation of the data I've seen...so buyer beware.
Among other gems the main spreadsheet contained actual pressure and velocity test data as tested by Tom Armbrust, for a variety of 16ga factory ammo. I have not looked over the actual test reports so I'm assuming things like temperature varied enough over different test runs that the data should not be used more than in a general sense, but I do know that the data represents average figures for 3-5 shots of each load--not 100% scientific, but the best source of info on this I've seen. Keeping in mind that this was for 16ga ammo only, some generalizations might be made: 1) a larger shot payload did not automatically equate to higher pressure, although there seems to be some correlation. 2) 2 1/2 inch shells do not equate to lower chamber pressure. 3) american shell companies seem to make shells that will cycle autoloaders, and their pressures tended to be on the higher end of things--usually. The tested ammo from rem/win/federal hovered around 10000 psi +/- 1000psi. European ammo companies had more variety, going as low as 7500 and as high as 12000+ (over the SAAMI max). 4) Even some of the ammo marketed specifically for older guns had pressures in the 10,000 to 10,500 psi range, although most hovered around 8000 psi.

To compound my confusion, when I spoke with a noted shotgun barrel smith a while back he discouraged me from worrying too much about pressure, and said that at least with fluid steel guns "in good working order" (to be defined by someone a lot more qualified than me!) it would be more worthwhile to worry about recoil to protect the old wood.

Seems to me that if this is something to worry about that the only way to ensure that you are shooting something of a known entity pressure and velocity-wise, is to either contact the ammo company and see if they'll give you pressure and velocity data (they won't all do this), send out some shells to be independantly tested, or roll your own from tested reloading data.

Last edited by David Furman; 03/30/07 04:35 PM.
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Just discussed in a recent thread
http://www.doublegunshop.com/forums/ubbt...ge=14#Post31794
Bottom line: I'd definitely keep the pressure below 9500 psi, which is easy today with all the 'Low Pressure' 12g and 20g commercial loads http://www.doublegunshop.com/forums/ubbt...ge=11#Post31805

Here's data from actual pressure testing:

3 Dr.Eq. 1 1/8 oz.
Winchester Trap Load
1,202 fps
9,600 psi

AA Xtra-Lite 1 oz WAAL12
1189 fps 8000 psi

Here's the B&P data (keep in mind that 850 bar is the proof pressure for a service (using) pressure of 650 bar)
http://www.bandpusa.com/files/db_trio.pdf

Last edited by revdocdrew; 03/30/07 04:32 PM.
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Chicago Offline OP
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David and revdocdrew: Thanks so much, I have that recent data on 16 ga, but I had no idea how that translated to 12 ga or 20 ga, if at all. I had thought that 2 1/2" shells had less pressure, but commentary and Revdoc's B&P chart sure reflects differently.

Revdocdrew: From your response I gather that as long as I stay below 650 BAR I should be using shells intended for this gun? Did you obtain the charts online, or ask for them from the company? Off hand do you know conversion factor for BAR to PSI?

On a separate note if an English gun is proofed for 1 oz and 3 tons does that translate about as follows for PSI. 3 x 2,240 lbs = 6,720 psi at (proof). 6,720 psi x .75 = 5,040 psi for use? I ask because I was recently lusting after a Watson Bros. BLE 16 ga with that proof.

Thanks again,

Chicago (Mike)

As my Marquette, MI hunting friend says "I don't know how many guns I have but I know I need one more"

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Oh my Mike: I was sure thinkin' Larry Brown would come along by now. I've tried hard for about a year to understand this, and still do not. The biggest problem seems to be that the bar, tons, psi numbers mean different things in different countries and in different time periods and there is no simple conversion formula. I DO have some conversions on this thread
http://www.16ga.com/forum/viewtopic.php?t=2642 but I'd read carefully what Larry added.
For those of us with simple minds, a ROUGH AND INEXACT conversion is 850 bar = 3 tons = 12,328 psi and based on a calculation from Burrard's "The Modern Shotgun"; 12,328 psi would be a proof pressure for a gun intended for a 8960 psi service (using) load. SO-as above, try to keep the psi below 9000.
And as always-remember pressure does NOT equal recoil, and it's the foot lbs. of recoil that is going to crack the stock.
If anybody else can help, PLEASE DO.




Last edited by revdocdrew; 03/30/07 07:46 PM.
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The RevDoc's synopsis fits well with what I've read of 850 Bar European (CIP) proof vs. service pressure. Feller that had what I can only refer to now as the defunct "Spanish gun site" on the web said 2/3 of proof for service pressure or about 8000psi. I don't remember ever reading anywhere a "rule of thumb" that proof pressure is customarily 150% of anticipated service pressure but that's the way it appears to work out with Sherman Bell's Remington (SAAMI?) proof pills: roughly 18000psi at proof for anticipated service loads yielding maximum of 11000+psi. The French "triple palm" proof pressure appears to be about the same as current SAAMI: 20Kpsi against 18Kpsi.

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Chicago Offline OP
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Hmm.......I am not sure I follow the math and it probably does not work that way, but I think I follow the general gist of things. I do really appreciate all of you posting on this issue.

Based on all of your observations I am more than safe on psi, and I was going to go to lower psi for protection of wood. But it sounds like lower psi is not necessarily lower recoil.


Any comments on poly-wad Vintager shells and actual recoil, or pressure? I know they have 25g shells that are about 6500 psi.

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Poly-wad and RST have great shells, low pressure, AND low recoil

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Chicago, one of the confusions regarding British proof is that the 3 tons per sq inch refers to a service pressure. When they switched to bars they also switched to proof pressure. A second area for confusion is the different methods used to measure pressure. The UK proof houses use crusher methods whereas in the US piezo methods are used. There is no direct way to interconvert the two, though there are some aproximations.


Regards - Ian Forrester
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Chicago Offline OP
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Revdoc: Thank you

Ian: It sounds like the older Brit guns were done in Tons and newer ones in BAR?

Is there a good book out there that deals with all of this? Not questioning responses, just trying to increase my understanding of British guns.

Thanks Chicago (Mike)

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