Looking a a few guns in the upcoming Holts Auction. Wall thickness of 15/20+; 17/17, 18/18, 23/17. And these guns are not estimated to be bargains but start about 2;000 and up. All in proof and legal to sell but buyer beware was never more needed. In proof is a poor guide as to true gun suitability for use. To me it is only the lowest hurdle that must be passed. Then wall thickness. Then on face. Then cracks or repaired stocks. The list only grows with the price.