Here's a cool trick.
Top off your ammo at an ammo dispenser.
Turn around and drop it on the ground.
Turn back and top off.
Repeat as necessary.
Also you can pick your weapon load out, get it and then dump it and all the ammo on the ground, go back into the HQ and change your load out package and pick it up from the quartermaster. When he gives you your new issue your old gear will still be laying there.
ALL the issue weapons are at 100% and don't seem to degrade.