There's no logic in going to the field with ammo stacks. I know this has to do with inventory management, but if you are a member of a security force, military, etc. You'd go to the fight with clips on your equipment.
The ammo should still be piled in stacks in the locker, but when you withdraw you should get clips or magazines based on the equiped weapon.
Sorry if my english is not that great. And greetings from Argentina ♥