Model 1873’s can be divided into 5 groupings.
Early First Model, serial no. 1 - about 28000
Late First Model, approximate serial no. 28000 - 31000
Second Model, approximate serial no. 31000 - 90000
Third Model, approximate serial no. 90000 – 720610
22 Rimfire Model - manufactured from 1884 to 1904
The Late First Model has two frame screws above the trigger pin, all 3 above the trigger. The Third Model did not have the frame screws above the trigger pin. The .22 Rimfire Model loaded through the front of the magazine. (From W L Wilson’s “Winchester, An American Legend”)