I totally disagree. If the gun is proofed for 70mm standard nitro proof, you should be perfectly safe shooting 2 3/4" 'normal' loads through your guns (the likes of Winchester, which we import and use for example).
Small Bore, straight from the Birmingham Proofhouse via email I received in 2001, when the standard proof for 12 bores was 850 bars (which I do not believe has changed, even though such guns are now marked "STD" rather than "850 bars"): "The reference in the article to the CIP service pressure of 650 bar and proof pressure of 850 bar is a reference to crushers values; the equivalent transducer values that should be used for comparison with SAAMI transducer values are 740 bar service and 960 bar proof, i.e. 10,730 psi and 13,920 psi."
The current service pressure standard for SAAMI-proofed 12 bores, either 2 3/4" or 3", is 11,500 psi. Proof standard is approximately 18,000 psi. Thus, SAAMI service pressure exceeds CIP standard service pressure by almost 800 psi. While a difference that small is highly unlikely to result in a catastrophic failure, if a CIP standard proof gun is fed a steady diet of "normal" American loads, wear might well result at a faster than normal rate. I would also point out that "normal" American 2 3/4" loads would include shot charges as heavy as 1 1/4 oz with a velocity as high as 1500 feet per second. Although most target loads are more reasonable in terms of both shot charge and velocity, the problem with stating that one is perfectly safe shooting "2 3/4" normal loads" through one's guns is that we keep pushing the boundaries of "normal"--which really only means anything that's not marked "magnum".
