The oldest .20 has a shorter 4.00” breach and probably uses the older style led seal valve with possibly the other photographed .20 has the new style 4.50” breach may use the cartridge style, though I haven’t disassembled this one yet.
Notes I’ve observed:
.20 Sheridan F9 S/N W131433 - I’ve read the “W” in the serial number is for Wisconsin. Notice the front sight is angled with a stylish knurl on the back taper (on both the large and small breach .20)
Nickel plated trigger and barrel length ends even with top of CO2 cap. Phillips screw holding stock to frame.
.20 Sheridan F9 S/N 118311 - Has a flat blade screw on retaining cap unlike Phillip on the earlier .20. Again, knurled back angled front sight.
4.500” breach. Barrel length again ends at top of CO2 cap. Flat blade stock to frame screw.
.177 Benjamin 397G S/N I010440 (G = Gas) - Black trigger and shorter front sight length. Flat blade screw on retaining cap. Barrel ends evenly with end of CO2 tube. Flat blade stock screw.
.22 Benjamin 392G S/N N022119 (G = Gas) - Black trigger and shorter sight length. Flat blade screw again on retaining screw. Flat blade stock screw.