I tested out Anti-Material rifles and marksman rifles and machine guns, yet none of those are able to fit into the big carryall backpack (I understand that the anti-material rifles wouldn't be able to realistically without dismantlement). Only the MX varients of rifles and marksman rifle and pistols are able to go into the carryall. I haven't tried multiple backpacks, just the carryall. I was just upset I couldn't have an EBR or Rahim and a MX assault rifle, and get fatigued after 10 steps.