yeah, no other item in the game directly modifies an ammo type both it's probability of dropping and how much you get. Even if you get a few drops it is more efficient because it has Surplus imbedded in with the perk, and it stacks with the weapon variant of surplus.
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Not many people actually realize you get more ammo per box. Most just assume they aren't working when heavy ammo isn't literally coating the ground. I tried to explain to someone once that the main focus of the perk is more ammo per box overall, but they were arguing the perk only increases ammo drops and that I don't know anything.