Ed, you might recall that our late friend Miller had told us of smoke checking actual contact of bolting surfaces in a number of guns with multiple bolting, and found that none showed full contact in all areas of bolting. In other words, only one or two were doing the work, and the rest were simply cosmetic.
A well designed shotgun can be adequately and safely bolted with a single bolt. The one I am most familiar with is the Syracuse Lefever, which does quite well with a simple single bolt engaging the top rib extension. Their biggest problem seems to be with top lever springs that become weak or broken, and then do not provide secure bolting. The bolts themselves are pretty simple, and fairly easily replaced when they wear to a point of poor engagement. Fox and L.C. Smith guns do pretty well with their single rotary bolts engaging the rib extension. But when fitted incorrectly, they are known to sometimes cam open when fired with heavy loads. Guns with a single well-fitted Greener type tapered cross bolt engaging the rib extension do very well too. I agree with Paul Harm that double rifles, which typically operate at much higher breech pressures, are more in need of well fitted and well designed multiple bolting systems. It takes a combination of good design, good materials, and careful fitting to achieve the most strength and durability. The guns that are prone to shoot loose and go off the face are the ones most likely to be deficient in one or more of these requirements. And of course, that sort of wear is accelerated by the use of loads heavier than the gun was designed to use.
