Why? What is wrong with the wad seater, powder bushing and shot bushing? Tht is adding WAY too many unnecessary steps to a simple process
Well slugs definitely don't go through a shot bushing, buckshot doesn't go through very well and large shot tends to hang up a lot of the times. Throw in adding an under shot felt, over shot felt or over shot card and it's just easier to load them off the press then deal with the on and off the press to get them loaded. I have not been able to throw Steel powder very consistent so I like to weight each charge. I can load 100 rounds just as fast as I load 100 rounds of rifle on a single stage so its no big deal and most of the time 1 to 2 hundred rounds of slug or buck is a plenty. Heck now that I am doing some roll crimping I only use a press for priming which can be done just by pushing the primer in the hull using a hard surface and a little pressure.
Guess you haven't loaded many specialty rounds before or you would know about the extras involved and issues with large shot in a small drop tube.