usually if you use cheats it makes you not be able to get achievement points.
i dont believe there are any. when you beat the game you unlock stuff. there are a few "glitches" i found for ammo, and money.
they may have fixed the glitch by now.

but...
chapter 2-1
by the humvees. collect the gold on top of the thing and get all the ammo. remove gun from inventory. and get another gun.
go outside the door, quit and save.
you can sell the gun