doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Pressure question

A simple question, I think. I recently bought a British gun and I plan on loading ammo for it. The gun is marked three tons, so I know I want to keep my ammo below 8900 PSI. I'm thinking I'll stay below 7000.

My question is this. What is the pressure level in Lup that I want to stay below?

I've tried searching for the answer and all I could come up with were complicated discussions without a clear answer.


Thanks, Tim

Congrats on the new to you gun.

I’m pretty sure the conversion of LUP does not correspond exactly to PSI. Are you getting reloading data that expresses pressure in LUP?

7000PSI is pretty low on the ammunition pressure scale. Bet you are fine with any ammunition around that point.

Good luck.

Best,
Ted

Tim, good question, but not a simple question at all. There is no direct conversion formula to convert psi to LUP, or vice versa. Supposedly, some of the so-called conversion formulas can be far enough off to provide dangerous and unreliable information. The best you can get is approximations that may or may not come close to being accurate.

I've gone down this rabbit hole before, and found much of the same goblety-gook that you are probably finding from internet shotgun experts.

Fortunately, it probably doesn't matter much because virtually all shotgun pressure measurements being taken today rely upon piezo-electric transducers, which react much differently than directly measuring the compression of lead or copper crushers.

Probably more than you want to know Tim.
In the 1954 British Rules of Proof the service pressure was expressed in TONS and was measured by LUP.

There is no mathematical conversion for LUP as measured by change in dimensions of a lead cylinder in a crusher apparatus and a Tarage Table, to PSI as measured by modern piezo transducers.
Adding 10 - 14% to LUP numbers works pretty well.

The 1954 Rules of Proof “Highest Mean Service Pressure” equivalent transducer values as converted from LUP by Burrard’s formula: estimated Long Tons/ Sq. Inch Lead Crusher Pressure (Cp) conversion to PSI (pound-force per square inch): (Cp x 1.5) - .5 = TSI, TSI X 2240 = PSI.
2 3/4 tons = 8,120 psi = 560 BAR
3 tons = 8,960 psi = 618 BAR
3 1/4 tons = 9,800 psi = 676 BAR
3 1/2 tons = 10,640 psi = 734 BAR
4 tons = 12,320 psi = 850 BAR

Great Britain joined the Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives in 1980 but the new Rules of Proof were not introduced until 1984. Lead Crushers were used however until 1989; the proof marks in BAR (and shell pressures) thereafter are PSI by transducers.

I don’t know what powder you are using but there a number of loads listed within your criteria utilizing Hodgdens Perfect Pattern. In my neck of the woods it seem readily available.

The plan is card and fiber wads, I have PB and 7625, and the load data is in LUP. I'll just keep pressures for that down around 7,000 too, I would think that should be safe.

Tim

Are you going to tell us about the gun?

Best,
Ted

Well, since you asked here it is. Joseph Bourne and Sons, 28-in barrels, 6 lb 11 oz, claimed cylinder and full, ejectors. Gun is in somewhat high condition , I suspect it's been in for regular maintenance. Action is absolutely tight and on face.

I tried, I sincerely tried posting photos. It's just impossible. If you know how to get the photos off Flickr, explain it to me and I will post them.

Tim

Tim,
Just email them to me, and I’ll get them up on the board for you. Just as an aside, I have to take them off of flicker to get them to work anyway. At the moment, the Brits that post here, and put up with us, can see the pictures with the service I use. That seems to be valuable when posting photos of English guns.

Perhaps one of them will have some better insight on your gun?

tedjs@usfamily.net.

Best,
Ted

____________________________________________________________________
Helps me to keep my curmudgeonly image here cemented.

I emailed you the pictures, at least I think I did, I don't know how the hell anything works on this damn tablet. If they didn't come through, or something is wrong let me know and I'll try again.

Tim