I was at first considering one of the bullpup designs to aid in recoil but my main goal is a large capacity 12 gauge (I have a Maverick Security that holds 8 already) and looking at the drum magazines which just will not work on a bullpup. You can go 10-round in a standard vertical magazine on a bullpup, but a 20-round drum just seems like something to have.
Besides recoil should be slightly aided from the semi-auto action, the one thing I have seen in my research is you have to be careful and test the ammo cause some shells won't cycle the action on semi-auto's. Basically, buy a couple boxes and run them through before trusting them in a self-defense situation.