For me, I found out the following things to provide a solution for this problem with Metro 2033:
The game has a max FOV setting of 90 – this is just about sufficient for a playable experience.
Any setting outside of the maximum range will cause it to default at 50.675
To change this setting you must edit “C:\Users\<username>\AppData\Local\4A Games\Metro 2033\<possible-generated-hex-number>\user.cfg” (Other installations may vary in location)
Modify so that “r_base_fov” has value 90.
Start game and enjoy (hopefully).