There are several reasons to proof a gun. In Mery ol', all new guns need be proofed. Europe requires that new guns also need be proofed, but since I once bought a rifle by a major Euro maker, and the damned thing would not chamber a round. I looked and the damned thing had never been CHAMBERED! It was, however, proofed! As it turns out, that particular nation only proofs a few out of a hundred guns. It would never happen in England as they never were much with bolt guns, so naturally, cannot be so trusted.
Of course, other reasons to proof a gun include when there has been a chamber lengthening, a honing beyond the proof limits, or when nitro proofing a Damascus gun. I don't know if the failed Purdeys may have been old Damascus guns with dangerously thinned and chamber lengthening barrels coming back for a nitro proof. That would make a lot more sense than brand new guns.
A bit on materials now. There are two different but very important steel strengths. One is Ultimate Strength. That is the pressure at which a piece of steel (barrel) will fail by blowing/cracking/splitting/etc. Another steel strength is Plastic Strength. This is the pressure where a piece of steel will expand to while under a load but return to the original shape. Over this amount, there is a plastic deformation, and the steel will be deformed. A barrel bulge is a form of this. The proof tests carefully measure the barrels at a number of critical areas before and after proof pills are fired. If there is any measureable deformation, the barrel has failed proof test. Of course, blowing a barrel is the worst form of failure. There is also the preliminary visual test by the proof house. The barrels fail if the barrels are loose to the frame, if they have bulges, or pits. They must visit the smithy and these things be fixed before the tests can continue.
Stuff happens (like the stainless Sako barrels in a certain serial number range of which at least 6 blew up). However, I would be very surprized if new Purdey barrels blew. It might make one send ones guns to Birmingham, instead.
Of course, this solves the question of which is better, LC's and Parkers or those Brit things. No LC or Parker has ever failed the London house. Proof positive, wouldn't you say, David?
