Posty,
I've been shooting the H&A set-screw style for years and never had any problems. I normally dimple the breechplug for the top screw and use a tapered screw so when you pull the barrel off or swap it with another barrel, the taper on the screw and plug bring it right back into place every time. On the H&A and my own actions, the breech end of the barrel buts tight to the action face plus you have the 5/8" dowelpin/breechplug going into the action, it's a far superior mechanical connection than the hook-breeches that were used on English guns including the huge-bore doubles. If you've ever messed with a Mowrey or similar rifles where the barrel is threaded to the action, they're a pain in the butt and you can't swap barrels without major hassles. Pinned barrels are problematic too, swapping barrels is a pain in the backside and when the pin hole wears or otherwise get buggered-up, you have to ream the holes and make your own pins - goes back to making things cheaper & faster on the assembly line. I don't recall who but at some point I saw an underhammer with a double-treaded breechplug, screwed into the barrel on one end and breech on the other. That's all fine and dandy but the slightest amount of wear on the threads, action face or breech face and you're barrel is not going to stop in the same position every time ... so then what? Shim washers?
The weakest point of any gun is the wrist and I've got that problem cured.