while the Model 1900 has a Baker J-spring snap-on/off forearm. Early Model 1900s have a smooth stock head while the later Model 1900s have cheeks just like the Model 1894s. At least on the later Model 1900s they didn't file down the breechballs to perfectly match the breech ends of the barrels, and one can feel and see a bit of a lip there.
There are a lot of things that changed over the 16 years Remington Arms Co. built hammerless doubles. The early guns came standard with a rather high flat rib with the option of a "hollow" rib on the higher grades. In the later years a "hollow" rib was standard on all the Remington Hammerless Double Barrel Shotguns. Early guns had firing pins integral with the hammers. Those guns have the sear and hammer pins in these locations as on this 1895 vintage BE-Grade --
Parts diagram 1901 Remington Arms Co. catalogue --
By at least 1905 they changed to seperate firing pins and the hammer and sear pins locations are a bit closer together as on this 1909 KE-Grade --
Parts diagram 1908 Remington Arms Co. catalogue --
Also, over the course of years, Remington used three different styles of barrel lugs.
Enough for the first lesson!!