I'll have my kid take a look at that site. I've found my .410 barrel on the G2 pretty effective even on quail, although I don't put it on when I'm actually after quail. But when I'm hunting cottontails with it, I've flushed quail a number of times and actually hit some! Not sure what the choke tube on it is: it looks to me like there is almost no choke in it! No markings on it at all (I got this barrel used).
I'd like to try a 28 guage barrel on the G2; think it would be even better than the .410. I use a Ruger Red Label 28 O/U for upland birds and shoot it better than any other shotgun I've ever had, including my Beretta 20 ga O/U and Ruger 12 ga Gold Label SxS.