doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com CIP specifications.

I still find it curious that proof pressures seem to be related only to gauge and chamber length. A gun made by the same shop, with 2.5" chambers cannot handle the service pressure of another from the same shop made with 2.75" chambers and identical lock-ups. Yet two guns made in different shops, much different in construction including locking lugs and barrel materials and thicknesses are proofed to the same pressures, if they have the same chambers.

I have never seen a good justification for this.

Think of it like law and rules. There are no selective exceptions for agendas, unless proftypes pretty much make upcow pies on the fly? Just kidding, if the stamp says all's good, then all's good.

In other words, you have not a clue. Got it.

A 2 1/2" chambered gun might stand up to service pressures of the 2 3/4" shell, no rule says it can't. A 2 3/4" live pigeon gun will probably be heavier/stronger than a 2 3/4" game gun even though they are both proofed to the same standard.

I look at it as being somewhat comparable to metallic pistol cartridges and ratings of "standard", "+P" and "Magnum". Standard 38 Special loads are just fine in your typical pencil barrel S&W Model 10, "+P" ammo is better relegated to the stronger Model 19. Moving up to "Magnum" loads belong in the Model 27 as evidenced by the number of "K" frame guns that were shot loose with magnum ammo.

.38 Special = 2 1/2"
357 Magnum = 2 3/4"
357 Maximum = 3"

Just my thoughts on the subject, certainly others are more learned than me.

It is reassuring that Sherman Bell's destructive test of the Parker Vulcan Steel VH and 3 Iron Damascus GH took about 30,000 psi to burst.
The GH testing started at 11,900 psi and one chamber ruptured at 29,620 psi. The VH started with a Proof Load of 18,560 psi. Both chambers bulged at 29,620 psi and ruptured at 31,620 psi.

Proof and standard service load pressures have not changed much in 130 years despite all the new fangled low alloy barrels.
Dense Smokeless did run about 1000 - 1500 psi higher than Bulk Smokeless

Forest & Stream, November 24, 1894
“Gas Pressure or Bursting Strain”
https://books.google.com/books?id=19kwAQAAMAAJ&pg=PA459&lpg
The proof-house charge of the American Testing Institution for a 12-bore gun develops a gas pressure of over 18,000 lbs. to the square inch. (By LUP so transducer number would be 10-14% higher)

English 12g service & proof pressures + 10-14%
Field, November 26, 1892
https://books.google.com/books?id=inQCAAAAYAAJ&pg=PA296

"E.C.", "Schultze". and "S.S" all bulk powders





Smokeless Powder Co.'s “S.S.” (Smokeless Shot-gun) was a 43 grain = 3 Dr.Eq. Bulk powder that didn't last very long because of pressures turned out to be higher in 16g and 20g

Drew,
Well, there is that, but, from where we are today, long removed from the manufacture of these old guns, the mechanisms that hold them shut and the very old wood they are stocked with, goes hand in hand with concern for the barrels.

My initial post had to do with why a 2 3/4” round carried CIP approval with a 1 1/8th ounce load, and it seems MODERN proof in England does not concern itself with the weight of the charge. Fair enough. You learn something new every day. Thanks.

I’ve no English guns at the moment to concern myself with. Again, based on Bell’s research, the old Halifax, .050” walls proofed at French single proof, with 2 1/2” chambers, originally cut for waxed paper cases, will happily digest them, I’m sure. The pressure won’t be out of spec for that gun, and the pressure rise from a 2 3/4” round in that chamber will be negligible. The Spanish double has 3” chambers. The Beretta O/U has 2 3/4”, with standard Italian proof.

They will work in everything, here.

Best,
Ted