Much has been made over the years of multiple bolts, inferring "Great Strength". Most of it is nothing more than Advertizing Hype. The main stresses on a break open gun are not in holding the bbls shut, but in holding the standing breech "Up To" the barrels breech, which an underbolt adds very little to. Thus the hinge pin takes the thrust & the strength of the frame keeps the standing breech from Flexing back. I think that both Parker Bros & Winchester 21s proved beyond any reasonable doubt that a single underbolt is ample to hold any double "Shut". It is not really a matter of "How Many" bolts a gun has but of their strength & how well fitted. In many guns having multiple bolts a check of their fits will reveal that "VERY OFTEN" a single one of them is actualy carrying the load, the rest being simply superflous. It should also be well noted the more bolts a gun has the more difficult it becomes to ensure that all are equally sharing the work to be done. It is also noted the further the bolt is from the hinge the less is the strain upon it, thus the forward bolt of a double bolt, even if equally well fitted can never carry the load of the rear bolt. While I have never actually seen a thumb lever Purdey in the flesh, as I recall its bolt does occupy the position of the rear bolt in the double bolted one. "IF" of adequate strength the one is all that's really needed.
