Glitch propably found by DeimosComaBlack youtube user.

Easiest way to reproduce this glitch:

1. Pick up chaingun in mission 2
2. Start shooting (keep fire buttton pressed through all steps)
3. Switch gun (you'll still have chaingun equiped, but HUD will show next/previous gun in your equipment)
4. When ammo count hits 0, you'll notice that weapon keeps firing. Switch back to chaingun.
5. You can now use Chaingun with unlimited ammo as well as any other weapon.

What happens is ammo count gets reseted to 65535. If you keep firing long enough, you'll notice graphic bugs on your screen. I'm yet to determine if it's dangerous to the run, but I had never soft-locked the game or encountered any game-breaking situations.