I'm trying to get my head around shotgun load pressures, my ADI & Hodgdon manuals give pressures for various loads with the powder I have typically between 8000-11000 psi. My two shotguns have proof markings which give me lower figures than these AFAIK. My Greener GP is proofed to 3.25 tons per square inch which as I work it out is 7280 psi, my Spanish SxS is proofed to 600Kp/cm2 which I think is about 8534 psi. I suspect I'm not comparing apples with apples somehow, can anyone elaborate on this?
Steve.

Let me be frank. I am not an engineer and this is buzzing a bit over my head.

My GUESS is: You mention Greener and Spanish SxS... were these possibly old guns from the black powder days? Black powder loads worked at much lower pressures than modern smokeless loads. The smokeless loads you cite are quite modest and soound like target loads or light field loads. If you examine the pressure data that is in some Hodgdon manuals for black powder guns, this is painfully obvious. Most work well under 10,000 LUP (lead units pressure. CUP copper units pressure measured with a copper pellet crushed are used for higher pressures, over 15K as I understand.)

b). Some guns were overloaded as a pressure test ("3 blue pills") then retested at working pressure and marked "proofed" as O.K. at these "working pressures" or so says the articles in several Gun Digest annuals I have owned.

c). As I recall, the Mauser 98 was "proofed" at around 80,000 CUP while it is expected to work safely and reliably up to 50,000 CUP.. Of course, soldiers are considered expendable and not of great worth...

I share your concern. Is there a date with the Proof marks? If these are old, old guns, they might only be suitable for "black powder pressure" loads. Luck.

It gets worse! Some of these old guns were chambered for the shorter shotshells and for roll crimp shotshells. You do not want to fire star crimped shotshells in those chambers - the crimp unfolds and enters the leade, which pushes pressures up considerably. Simple enough to check.

There are some very low pressure 12 ga loads out there in the 4000 to 5000 psi range. I think sr4756 or 7625 is use to make them. They work well. 4000 to 5000 psi is in the range of black powder loads.

I'm assuming that these are 12 gauge guns.

If you go to the IMR loading manual, for example, you can find 1 ounce 12 gauge loads, using Winchester AA or Remington hulls and the Claybuster 1100-12 wad (a wad designed for 1 ounce loads), and using 700X, or PB, or SR 7625, and loaded for 1100 or 1150 f.p.s. velocity -- all you really need for most target and upland game shooting -- that are 7,000 psi. or less.

If you load and shoot such loads for awhile, you will, I think, begin to wonder why you thought you needed those heavier loads.

If you go to the Hodgdon manual, you can find similar 1 ounce loads at 1125 f.p.s., using Titewad or Clays or International powder, and giving under 7,000 psi.

Again, I don't think you need more than 1 ounce of shot at more than 1125 f.p.s. or at most 1150 f.p.s. for a lot of shotgun shooting.

I'll throw another one out there I believe that the britsh guns were proofed for "long tons".

quote:

Originally posted by shorthair:

I'll throw another one out there I believe that the britsh guns were proofed for "long tons".

A long ton is 2240 pounds. So if the British guns were proofed for long tons, their ton would be larger than the regular avoirdupois ton -- the one used in the US. Thus they would actually be proofed for slightly more pressure than would be the case if that ton were interpreted as a "regular" ton, which is 2000 pounds.

Don't know if this will help, but just FYI:

SAAMI Max Average Shotgun PSI:

10 ga - 11,000
12 ga - 11,500
12 ga(3-1/2")-14,000
16 ga-11,500
20 ga-12,000
28 ga-12,500
.410 bore-12,500
.410 bore(3")-13,500