Welcome to the forums. :)
Hopefully I can assist you with your problem. It seems for some people that there is a weapon bug. However, there are some things you can do to see if you have it or not.
When you join a server, make sure it’s an official one if you want to put kills towards unlocking the next weapon as unofficial servers may have this turned off. Also, if you join a server and find that the number on the next weapon you want to unlock is not going down then you may need to restart the game or Steam it to start to count.
Hopefully that fixes your problem and you’re not hit with the bug.
If you have any other questions, complaints or anything then feel free to post them and either myself, another moderator or a fellow community member will do our best to help. :)
This happens to me pretty much consistently, regardless of restarts, reconnects, ect… I cannot progress and I’m going to have to find something else to play until they get this fixed… I was going to buy the expansion, but I don’t see any point as I’ll probably not be able to use half the weapons. xD