Thank you for that very cogent explanation. It is very helpful. My point was only that a gunmaker, for commercial reasons, might not necessarily request the highest proof, even though the gun in question might be able to satisfy the higher proof test. Incidentally, how does one ascertain what the pressure of one's ammo is? Is all standard 2-3/4 inch US ammo roughly the same? Does it make any difference if it is Rio, Winchester, Fiocchi or Estate (I.e., foreign or US manufacturers or licensees)? Is the SAAMI standard a maximum? P. S. When you feel up to it, I wouldn't mind a short course on other countries' proof houses. Interesting stuff I think. Thank you.
HOS, the only way for sure to know the pressure of your ammo is either to reload very accurately and go by what the book tells you, or else--if you're shooting factory ammo--send some off to someone like Tom Armbrust for pressure testing. (You can do the same thing with reloads if you vary somewhat from a book recipe, maybe in an attempt to lower pressure even more for vintage guns.) The SAAMI standard is a maximum, although there can be some slight variations above that max. Without having specific American loads pressure tested--and I'm speaking Winchester/Remington/Federal, not the small specialty makers like RST, who will provide that information--you are stuck with the assumption that the loads may be as high as the SAAMI maximum. And even if you have a particular type of shell pressure tested, there's no guarantee that the next lot of the same shell will have the same pressure. American ammo makers load for consistent velocity, and they occasionally change the powders they use, which can mean a pressure change. Makes no difference to them as long as they stay under the SAAMI standard and maintain the same velocity. British/European shotshell makers will sometimes provide pressures for their shells. But the markings on their boxes often don't even include velocity, although they do tell you for what kind of guns (chamber length/proof pressure) the shells are intended.
All the proofhouses within the CIP countries (which is the blanket organization to which the British and all the major European gunmaking countries belong) conform to the same general proof and service pressure standards. The problem is that they all use their own proofmarks, which are sometimes pretty clear (as in when they give you a proof pressure figure in bars), sometimes not. The really confusing part is that all of those countries have changed proofmarks several times in the last century. In the case of the British, starting with the proof rules of 1925, there have been 4 major changes. And if you have a really old Brit gun, there were several changes prior to 1925.
