I have been through the shot bridging aggravations, too, Tom. I found the best solution to be the same as you, tapping on the drop tube. Thanks for the suggestion on the 700.
I had decided earlier that this would probably be my route, hence buying the .410 collet for my SuperSizer. I knew with the small chambers on two of my .410 guns I would need a collet type sizer to get the heads small enough. I was fortunate and recently bought a flat of 3" loads of 7 1/2s for $110, but I can do considerably better than that by reloading. In my estimation, reloading .410s is worth the troubles it entails.
Thanks again, SRH