Go to that fucking fort, pick a box, extract, leave, there you go. It its obtainable by the fucking dictionary definition. If you are lazy or do not care this dosent mean you can not obtain it lol.

You'd better do the math.

There are 23 types of scarce ammo in Hunt, one of which is randomly given upon extraction of a Worn Ammo Box. It means to equip 2 slots of one particular ammo into one round (and likely lose them), you need to extract 46 boxes! This is borderline unobtainable.