This mod adds the Remington Model 1875 to the game, with scratchmade model and textures. It can be found inside the safe of the Commonwealth Bank near Faneuil Hall (see Video). It's a unique weapon, it can't be found anywhere else (with Raiders, Gunners, in chests etc.)
An alternate way to get it is to open the console and type 'help remington 0'. Note the item ID of the line where it says 'WEAP'. Then type 'player.additem [fill in the ID without brackets].

It's quite an overpowered weapon compared to the ordinary .44 (and most other vanilla weapons). No bullet-sponges with this gun.

I added 'Custom' to the name because the original 1875 Model had a fixed cylinder. Unfortunately, as I have no idea how to edit Fallout's animations (I hardly even get how textures are working in this game), I had to go with the default loading animation of the .44
Also there are no modifications for the workbench, you'll have to go for the Ivory-Nickle combination.

Credits go to

covadonga - His mod 'Remington 1858 New Model Army' gave me the idea, my mod is based on his. There are still some remnants in the esp. file, and also the gun firing sound is the same. Thank you for your permission!

Some other mods used in the video are:

'Bullet Time' by registrator2000
'Toggle Revolver Fanning' by shavkacagarikia
'Terminator Synths' by SecretAgent99

This is a project I made in my rare free time, please don't expect extensive support. Also I'll take no responsibility if your computer explodes using this mod. That said, the mod works well for me, I dont't have any problems with it.