If you hit an XM1 (GM) and damage the barrel, chances are all the shells will just disappear. This is not an ammunition burnout, but just disappear, even those that are lying on the bottom of the tank.
Had this issue two times in a row! No ammo rack, and only one of the two times did I have to repair…yet ALL ammo gone. Had this in the sepv2 also. More USA hate, lol.
can this be reproduced? if so, file a bug report
chances are they will get on it since its a premium