When you switch special weapon your special ammo supply depletes to zero. I assume developers have done this to stop players switching from shotguns to snipers etc too quickly. I don't think it is necessary though, since you have to go through the options to switch anyway, so your hardly going to do this under fire. It's just annoying.
Edited: 7/24/2014 6:20:37 AM PermalinkI think thats a bug and hope it gets fixed. I did it underfire In the last phase of the Last Array I switched my Hunters special weapon from Scout Rifle (10 rounds) to Shotgun I picked off a Thrall from an earlier wave. Had Thralls Rushing me and I Pull the Trigger and I have no ammo. On respawn my Special then had 0 ammo. Changing Loadouts to deal with variations of a scenario in a fight should be an option during your legendary adventure. Was the most fun I had in the beta sofar though