This happened to me and my accounts were linked. What I had to do was to wait a couple of hours, log out of Battlelog and re-log into battlelog and Battlelog finally showed my single player weapons. Just to clarify, The MP412 rex, the shank, the Machete, the P-90, the M249, and the QBB-95B-1 are the only single player weapons that carry over to Battlelog\Multiplayer. All other weapons that you find in the campaign that go into your weapons chest are just for the campaign and must be unlocked via normal multiplayer play to unlock for use in multiplayer.
