There are plenty of cool weapons in Fallout 4 and its a universe in which there's no lack of inspiration for a wealth of interesting ideas, so it's a little odd to think that a cool idea for a weapon could be cut from the game. Nonetheless, that's the case of the Harpoon Gun or it was before a modder discovered the files for it.
Modder xxdeathknight72xx was the one to create the Harpoon Gun mod, which takes the files of the Railway Rifle and swaps them with the scrapped files from the Harpoon Gun. The gun is fully working and it can take a person's head clean off and skewer it to a wall in a bubble-trailing line of doom. There's no ammo in existence in the world for the weapon, so you have to use a console command (press '~', type 'player.additem 000fe269 50', and hit enter to spawn the harpoons.) You can see it in action in the video below.
It's hard to say exactly why a weapon that was pretty much complete would be scrapped from the game. Maybe there were plans to implement it in the future or maybe it was just close enough to other weapons that the idea was deemed redundant. Either way, you can now spear some domes as you please with this mod. Keep in mind though, it's a mod based on a scrapped idea. There's no telling where things could go wrong with it.
You can find the mod at Fallout 4, check out our where you'll find this and other great mods we've uncovered.. To see other cool mods for