There's an increasing number of hunters using 28 gauge for turkey hunting with 18g/cc shot. The loads I've seen for the 28 have ranged from 1.25 oz to 1.5 oz. I know of a couple guys using o/u guns in the 28, but most are using semi-auto. I haven't heard of anyone using a 28 gauge sxs, but there is probably someone doing it.

Of course, all of these guys are using modern guns that can handle the loads. All the loads are pressure tested and within SAAMI specs. I use a 20 myself.