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Sidelock
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Pressure peaks within or slightly past the chamber. Ten inches down the barrel everything is under 1,500 psi, at 5” you are just over 2,000 psi. So your highest pressures are within an inch of the chamber, dropping off very quickly there after.

I spent a lot of mental energy figuring out safe loads for all my doubles. I shoot low pressures to protect the stock not because I think my barrels are too weak to withstand the pressures. Ultra thin barrels are not going to be shot by me. Terms like proof and service pressure help define loads to use. Black powder loads give you a safe working pressures if you need more guidelines. Most are in the 5-6,000 psi range.

My 12 bore, low pressure loads, run from 5,000 to 7,000 psi. Anything in between works well and I feel safe shooting them in all my guns. I have had less consistent results using sub 5,000 psi loads so bump it up to 5,000 plus. In 20 bore I top off at 8,000 psi but could go 8,500psi. Pressures run higher in small bores. I shoot 2 1/2” in 2 1/2” chambers but accept others safely shoot 2 3/4” in their guns. It is just so easy to trim a bunch of hulls and load shorter ones, plus I enjoy the process.

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Sorry. Not paying attention

Hunter Arms Co. Pressure Curve dated June 10, 1929, from the McCracken Research Library, Buffalo Bill Center of the West (found by Gary Rennles) and used by permission
http://library.centerofthewest.org/cdm/singleitem/collection/WRAC/id/8149/rec/107

The digital image is part of the Winchester Repeating Arms Company Collection but includes a notation “Hunter Arms Co”. WRAC was acquired by Western Cartridge Co. Dec. 22, 1931, so it is impossible to know if the curve was generated by Winchester, Western, Hunter Arms, or (very possibly) the Burnside Laboratory of the E.I. du Pont de Nemours & Co.

[Linked Image from photos.smugmug.com]

PROOF LOADS
Loaded with FFFg black powder. Shot presumed to be No. 6.
Pressures were measured by crushers (LUP - Lead Units Pressure) and modern piezoelectric transducer measurements would by 10 – 14% higher
F - 10g 2 7/8” 9.5 Drams with 2.36 oz. shot = 16,000 psi
A - 12g 3” 8.265 Drams with 2.187 oz. shot = 17,250 psi
G - 12g 2 3/4” 7.53 Drams with 2 oz. shot = pressure not recorded
B - 12g 2 3/4” 6.5 Drams with 1.687 oz. shot = 14,200 psi
C - 16g 2 9/16” 6.5 Drams with 1.687 oz. shot = 13,750 psi
It seems likely the ‘B’ 12g and ‘C’ 16g labels were switched
D - 20g 2 3/4” 5.74 Drams with 1.5 oz. shot = 14,625 psi
E - .410 2 1/2” 2.377 Drams with .624 oz. = 15,625 psi

MAXIMUM STANDARD LOADS
1” peak pressures
H - 12g 3” ‘Record’ 1 3/8 oz. shot presumed 1275 – 1295 fps = 13,250 psi
I - 12g 2 3/4” ‘Field’ 1 1/4 oz. shot presumed 1330 fps = 10,750 psi
The label ‘J’ for 28 gr. Ballistite and ‘K’ for 3 1/2 Drams DuPont Bulk appear to have been switched on the pressure curve graph. Dense Ballistite clearly generated greater pressure than DuPont Bulk.
K - 12g 2 3/4” 1 1/4 oz. 28 gr. Ballistite = 12,900 psi
J - 12g 2 3/4” 1 1/4 oz. 3 1/2 Drams DuPont Bulk = 10,000 psi

The pressure curves essentially meet at 5” at 7000 psi; at 10.1” 2625 psi (DuPont Bulk) to 3000 psi; at 15.5” 2000 psi; at 22.1” 1500 psi

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Jon, my understanding is that recoil, not chamber pressure, is what damages stocks. Velocity, a factor in recoil, is independent of pressure. A low pressure load of 6000 psi shooting 1 oz. at 1300 fps in a 100 year old double is far more likely to damage wood than a higher pressure load of 8000 fps shooting 1 oz. at 1050 fps. Gil

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well, well then, an so on, etc...

if max pressure is around 7" from the breeches, why then does no one else seem to care about minimum barrel wall thickness gudelines in front of the chambers...

cept for yours truly...

Last edited by ed good; 11/16/22 01:20 PM.

keep it simple and keep it safe...
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and how does one measure individual shotgun recoil...

presume it is measured in foot pounds per ?


keep it simple and keep it safe...
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Come on Ed, you know how to measure recoil.
I've been shooting Damascus barreled SxSs since around 2000. I try to keep my reloads around 7500psi which is fairly easy to do with 3/4, 7/8 or 1oz loads under 1200fps. That will also satisfy Ed. There are very many loads in my Alliant handbook for 7/8oz loads [ it's what international skeet and trap loads are limited to ] using Clay Dot, Promo, Red Dot, American Select any where from 6000psi to 8000psi, many in the lower range. You want to use fiber wads, go right ahead. You're just going to lower the pressures given with plastic wads. The fiber doesn't seal as well.
A number of years back Sherman Bell tried to blow up 20 Damascus " wall hangers " given to him. He used Remington proof loads of around 18,300psi. NONE of them even cracked. He then took a Parker to 30,000psi before it let go. He also tested longer shells in short chambers. Pressures went up about 500. I shoot 2 3/4" shells in all my 12ga guns, many have 2 9/16" chambers. I think the OP is worrying too much. I'm not saying all guns are safe. Use your own judgement.

Last edited by Paul Harm; 11/16/22 01:45 PM.
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I would go to Alliants and Hodgdons web sites, find their phone number, and give them a call asking for one of their free handbooks. I find them much easier to use then the web sites. You'll also get more info than Lymans hand book.

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"if max pressure is around 7" from the breeches..."
Is that a typo ed? and a shotgun "breech" is not plural.

Every published pressure-distance curve, including the one I posted, shows the peak pressure to be 1-2" from the breech, even with 'Progressive Burning' DuPont Oval.

[Linked Image from photos.smugmug.com]

[Linked Image from photos.smugmug.com]

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GLS, you are correct, low pressure, modest payloads, modest velocity do all play a part in protecting stocks and not stressing thinner or weaker barrels at the same time. Many old barrels are well able to withstand anything reasonable you put in them. 100 year old stocks might not. I just find a ounce, 1100-1200fps, at 5,000-7,000 will do everything I need it to do. I am not pass shooting geese at 70 yards with a short chambered 12 bore. I have a short chambered 10 for that.;).

I shoot a lot of Sporting Clays, Skeet, Trap and late season Dove with guns suited for modest, low pressure, low velocity shells. To easy cartridge identification all my Federal “short” shells are 1 ounce, number 7 1/2, 1125fps @5,600psi. My Remington load is 1 ounce 8’s at 6,500psi and 1150 fps. The Winchester hulls are 1 ounce, 9’s @ 1125fps. B&P are 7/8 ounce, number 8 1/2’s, 6,500psi @1250 fps. Every load was found on Hodgdon website. It takes time to gather different powders and wads but once done you can make enough ammo for months to years of use. I am not stressed by component shortages or ammo choices not being what they once were.

I load on a Spolar,in large batches of several hundreds to a couple thousand at a sitting. In a single sitting I can load enough to last for a long time and just keep stuff in buckets until I get around to boxing things up to stack on my ammo shelves. So whenever I pick up a loaded “short” shell I know automatically what is in it and that it is safe for every gun I own. If it is 2 1/2” it is safe for everything and I can just select different loaded shells to get the correct shot size for what I want to shoot. The B&P work great on Skeet with real crushing ink dots in tight chokes. It took a bit of planning but now I am never in doubt what I have on hand and have several thousand shells loaded for quick selection and fun use.

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While 2 1/2 data is the ideal, I have found that using 2 3/4 data rolled crimped into 2 1/2 length hulls works well. Sometimes I discover the load does not fit, but most times it does.

I simply stick to sub 8,000 PSI data as a rule of thumb. I have found Hodgdon’s website a decent source and there. I found their 1 1/8 loads for federal paper hulls and Remington Fig 8 wads and International powder good. I also like their Green Dot, PB, and SR 7625 data, though finding the later powders if you do not already have it is hard.


Michael Dittamo
Topeka, KS
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