Very interesting thread.

Couple things:

First, regarding the statements that no dimensional change is allowed as a result of the proofing process, I guess it depends on the proofing process. In its discussion of the proofing of service Lee-Enfield rifles, the British "Textbook of Small Arms 1929" states that in fact some measurable dimensional change does occur as a result of proof and it is intended to do so. That is, the proofing process was partly used to seat the locking lugs, etc. Additional machining to final dimensions was conducted after proofing also, another curious event I always considered a "no-no".

Second, I watched rifle proofing at the Musgrave Mauser plant in Bloemfontein, RSA in 1985. I may not have seen the entire process, but what I saw was this: A rifle was hand-held in a steel box, a round of ammo chambered, the lid to the box closed and the round fired by hand. I believe IIRC two rounds were fired per rifle. This occured very quickly and thus a number of rifles were tested in a short time. The rifle was then handed off to another guy and it was visually inspected, but I at no time saw any measurements taken of the rifle. The whole process was very fast and, to a layman, "unscientific". It is certainly possible that rifles were measured for dimensional changes when I wasn't present, but I didn't see this occur and it was my understanding at the time that the process I saw was IT.

I have a gut feeling based on my observations and the comments of Bramble above that "proofing" may not be the exact science some would believe, and in fact, functional testing of a sort may be exactly what it demonstrates, particularly in the absence of pressure-tested ammunition. I read somewhere else a description of proofing quite similar to Bramble's also, with similar comments on the fact that the actual pressure of the ammo used to proof the gun was unknown.

We must remember, that whether our rifles are proofed or not, we may nullify the relevance the proofing may have had every single time we work up a new handload. Truth is, most of us have really no clear idea what pressures our handloads generate, only that they work and don't result in a face full of flying metal.

Indeed, in some cases {pun intended} the proof process may tell us more about the brass case than the gun. Looking at it from the other side, I read once a comment by an astute observer that looking for pressure signs on cases may be immaterial in guns that are "weaker" than the case, meaning of course that by the time we see significant pressure signs on the case, damage may have already been done to the gun. A case may fail at 70,000 psi, but if the strength of the action is 65,000 psi, well, you get the picture. And putting it another way, testing the ability of a really strong action to handle a ruptured case by purposefully weakening the case before firing it would be a nice aspect of proof but it is, of course, not done. Truth is, we trust the gunmaker in many ways, and those who think their gun is "safe" because it was "proved" may be deluding themselves a little bit more than just a little bit.

I'll go so far as to say this: "Proofing" demonstrates only that on a particular day Gun A was fired with Load A and it didn't come apart. We cannot assert how many rounds of Load A Gun A will fire before letting go and we cannot assert that the mere firing of one or two rounds of Load A means the gun will safely stand some number of rounds of Load B. That is why the specific load is marked on the gun as proof.

In effect, those of us that are handloaders "proof" our guns every time we work a load up and we shouldn't forget that. The safety margin of design and material is an unknown quantity.

As for American guns being proofed, they are. "After the fact" they are proofed by judges in courts of law. I submit, as much as I am disgusted by our legal process in-general, that this method is every bit as effective as that produced in other nations' proof houses.

And a final case in point: Every low number Springfield rifle that blew up in its firer's face whilst firing regulation service ammunition had passed "proof" before issue. And so had all the recalled SAKO 75's...