The rider gun uses Sniper ammo, and always generates 1 ammo even if your empty. Its Semi-Auto, fast, and accurate.
When you OBTAIN (do not complete) the quest "another piece of the puzzle" (I believe you get this right after doing the "cleaning up your own mess" or "brotherly love" quests)
You can go to a house in new haven, And a door opens up! There's random loot, lvl 30 raider mutants, and always 1 of the weapons is a gun named "rider" stats usually vary a tiny bit each time u get one (only located in this house!) The weapon's "manufacturer" is "Gearbox" (the developers) as opposed to an ingame company like Dahl, Hyperion, etc.
If added onto my other "infinite weapons money etc. video", the town of new haven really pays off!