It's possible to acquire a Storm Bolter pistol with 10 out of 9 bullets loaded.
If you reload it, it gets filled to 265/9, and if this would cause you to consume an ammo stack, that stack is instead filled to 65536 minus the ammo difference. If you drop that stack and pick it back up, it's converted to 250 ammo and stacks normally again. If you put the Storm bolter from your hands in your inventory, it gets reduced to 75/9 ammo.
If you ever fire enough bullets to drop the ammo count below the max, it functions normally again.
Howto:To reproduce this bug, build a Storm Bolter with 2 bulk for a X/10 pistol, reload, then add the technical. The resulting gun has 10/9 ammo loaded.
Image:(http://i.imgur.com/9eA9F.png)