On the Zombies armory, I can't apply attachments to certain guns, such as the KAP 45, the Daemon 3XB and the Swat RFT. Do I have to unlock the guns on Contraband tier system? I'm tryinng to unlock all guns for darkmatter camo but I can't complete some of the technical challenges on the aforemnetioned guns. Furthermore, I can't even apply attachments to the MX9. I can't left click the gun to add any attachments even though I have unlocked all attachments and it's not a gun from contraband.