Proofing is an interesting situation. I am reminded of a Sako rifle brought to me by a new buyer. He was wondering why he could NOT chamber a round in it. It had been proofed but the chamber had NEVER BEEN CUT! As it turns out, Sako only has to actually proof 3 of every 100 guns. Hmmm. At one time I worked for a big box store and problem guns were brought to me. In 6 months, I had 6 Rem 700 short magnums returned with all exhibiting overpressure situations with FACTORY AMMO! Most could not extract the round. The guns were sent to Remington and all returned either fixed or with replacement guns. There was never an explanation. Hmmm. The fat cases with little angle are a promise of over pressure.
Sherman Bells experiment was very interesting with rather little pressure variation between 2 1/2" and even 3" (600 psi as I remember). Also the barrels of Damascus and regular steel bursting finally at 29500-30,500 psi was also very interesting. In the case of doubles, I think there is little danger about which to worry but lots of value about which to worry.
