I'm calling this a 1928 Trojan though the movement is obviously 1927. Fifteen jewel, 10AN movement is consistent with the other, earlier models in the database.
The watch is 27.6mm (width excluding crown) X 28.7mm (length excluding lugs. The band is 14mm and, though its obviously old, I very much doubt its original as the buckle is gold.
Can't tell if the dial or cathedral hands are radium. If they are, they don't glow in the dark anymore.
1928 case with a 1927 movement is perfectly fine. Late 1927 would have been one of Bulova's busier and most successful years, so having a large quantity of their workhorse movement the 10AN, makes absolute sense. They were still using these into 1928 and 29, housing them in new cases/models for that year. Despite having an earlier movement we still date the watch by the case manufacture year.
1928 Bulova Tojan for me.
You can read about the Bulova Patented Dust-Tight Protector here.