The crux of my argument.
A "flat-bottomed" Fulton gun on the left (1901 "D" Hammer) and the heavy frame bolsters of a Syracuse-derived Quality 2 gun from 1890 (1st year at Fulton). Mr. Williamson is correct here. The breech balls are more angled than on the earlier Syracuse guns (page 88 in Houchins book makes that distinction fairly clear).