doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Birmingham Proof Pressures 1904-1925

The problem with pressure figures from US loads is that they do not remain constant from lot to lot. American ammo makers load to a velocity constant, not to a pressure constant. They don't always use the same powder, so pressure will vary. But as long as the pressure does not exceed 11,500 psi for a 12 bore, they're good to go. But if they say the velocity is 1330 fps, for example, that's going to be pretty close.

The other issue that needs to be emphasized here is that the "tons" marks were service pressures, not proof pressures. They were replaced by bars (850 bar standard, 1200 bar superior or magnum in the case of 12ga guns), and those were proof pressures. HOWEVER . . . in both cases, those pressures were measured with lead crushers, not piezo-electronic transducers, and therefore cannot be converted directly to psi because those are transducer-derived numbers. In the case of the bar proofmarks (or kg on other foreign guns), those CAN be converted, if you multiply x 14.5. HOWEVER, the result--if you start with bars as measured by crushers--will be LUP and not psi. More recent guns from Spain, for example, do show proof pressure figures in excess of 1300 kg or bars. Those are transducer measurements, and can be converted to psi--or at least reasonably close (there is apparently some variation in their transducer measurements to ours)--with the x 14.5 formula.

Complicated subject. I have never seen anything confirming proof pressure on pre-1925 British guns. However, a retired proofmaster confirmed that the proof loads used under the 1925 rules were essentially the same as those used under the 1954 rules, when they were marking with "tons" figures. And since he was proofmaster before the changeover to the 1954 rules, and for some time after, I think he's a pretty reliable source on that score.

Discussed at length in The Gun and Its Development, 1907
http://books.google.com/books?id=3HMCAAAAYAAJ&pg=PA280
See p. 293-294

"But as long as the pressure does not exceed 11,500 psi for a 12 bore, they're good to go. But if they say the velocity is 1330 fps, for example, that's going to be pretty close."

Larry with the different loads out there now, you can no longer state what you wrote above. As you can see from this recipe from the Alliant site, this is pretty close to your 1330 fps and nowhere close to SAMMI.

This load is for 3/4 oz. shot using 12 gauge Remington Gun Club or Nitro hull.

16.0 Extra-Lite Rem. 209P CB0175-12 1310 7300

I use a load similar to this using Titewad instead, the fps is a little slower.

Tim, I see you are in BC. Wanted to let you know I have no trouble having my gunsmith order a flat of Gamebore whenever I need one. I think if you find a non big box retailer who does carry Kent, you will likely have no problem getting some Gamebore. RST does not export so they are not available here.

Nice gun!

Here is the aforementioned book available online, you can either read it online or go to the second link, open it, then click on the .pdf version on the left hand side of the web page and when it opens, save it as an ebook.
Tim

The Gun and it's Development

Archive.Org Site

Thanks Canvasback. I went to the Kent Cartridges website, and found that there is a small dealer in British Columbia that sells Kent, Gambore cartridges. I will contact him. Wholesale Sports, Canada was the big box retailer that wasn't interested in helping me even though they sell some Kent Cartridges.
Thanks.
Tim

JDW, you're misinterpreting what I said. I'm referring to FACTORY shells, not reloads. But my point is this: Just because you test a particular factory load and find that it produces a pressure of, say, 9,500 psi, you cannot be confident that the exact same load--same company, same shot charge, same velocity (or dram equivalent) marked on the box--will produce the same pressure if it comes from a different lot. Ammunition makers vary the powders that they use. They don't worry about pressure, other than to make sure that they stay under the 11,500 psi SAAMI service pressure ceiling. The next shell you have pressure tested may develop 8,000 psi or it may develop 11,000 psi if those shells are from different lots. But they will all be quite close to one another in velocity, because velocity is the constant towards which the ammo companies work.

Even though my point was in reference to factory loads, it's easy enough to confirm by looking at reloading books. You can have higher pressure loads that produce lower velocity than lower pressure loads. And you can have a higher pressure load and a lower pressure load that produce the same velocity. If we shoot vintage guns, we worry about pressure. Winchester, Federal, and Remington do NOT worry about pressure other than not exceeding the SAAMI maximum because their loads are not designed for our guns. Their major concern is sticking to whatever velocity is marked on the box. RST, on the other hand--making shells designed for our vintage guns--will focus on pressure. For obvious reasons.

Tim Cartmell,

You might check to see if B&P (Baschieri & Pellagri) has a distributor in Canada.

They make several hunting & target loads in both 2 1/2" & 2 3/4"
that would be of appropriate pressure for an 1 1/4 oz /2 3/4" proved gun.

Their shells are of excellent quality & they list the pressure of their loads under the CIP standard.

Thanks everyone for all the great info. Good post Larry, thanks for the explanation about American ammunition, makes sense. I will try and round up some Gambore english traditional loads that will be about my only bet. I haven't came across any other european made shot shell ammunition in Canada, no B&P (Baschieri & Pellagri) here to my knowledge.

Tim

The short answer to the practical problem: buy CIP rated cartridges with cases of 70mm or less in length (not 'Magnum').

Stick to a sensible load for the weight of your gun (probably 1oz or 1 1/8oz).

If available, any of the following will work:
Hull Imperial Game
Hull High Pheasant
Gamebore Pure Gold
Eley VIP
Eley Impax
Eley Grand Prix
Kent Classic Game
RST 2 1/2"

all these are made to be safe for se in the gun you showed us, as long as it remains in proof.