Beat the "Tanker Chapter" and collect 30 dog tags. Look into your items and you should find "Solid Snake's Bandana"
put it on and you will have infinite ammo. Note:If you get shot the bandana will dissapear and you will have to put it on again. You will also have to reload.
We have more cheats and tips for this game here, Metal Gear Solid 2: Sons of Liberty cheats
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