As I said above, the H & D Folsom Leaders and Black Beauty Specials appear to be in their own serial number range. Those I've recorded are from 4020 F to 17275 F.
4049F 04.jpg
The Paragons and above appear to continue in the 20xxxx range from the Baker Gun & Forging Co. R- and S-Grades and later round cross-bolt style Paragons and above. The R- and S-grades were gone well before the sale to H & D Folsom.
Now, just to add to the confusion, I just looked in another file and found pictures of an H & D Folsom era Black Beauty Special with a serial number 201255 F --
201255F 01 BBS 12-gauge, 30-inch.jpg
201255F 02.jpg
Hybrid Mode