If you find any unlockables post them here
There are alot of weapons listed in the model viewer after completing the game but no one seems to know how they unlock. So far i know that...
Beating game on any difficulty unlocks Rocket Launcher and Machine Gun and 2 new difficulty modes
Beating game on nightmare or akumu difficulty unlocks Brass Knuckles
Collecting all map fragments unlocks burst pistol and high powered rifle.
The only one I can't figure out is how to unlock Joseph 1911 pistol
If anyone else has found anything else please share