Here's a tip for unlocking the f2000 on metro.
1st get a assault rifle ribbon, can be on any map and it doesn't reset after you achieve it.
Number 2 and 3 need to be completed at the same time.
2nd you need 2 assist ribbons. I tried a few (many) times to get this and this is what I found to be the easiest. Use a semi auto shotgun with frag rounds, you get alot of hit markers and therefore alot of assists. Use the noob tube(320), sit back on a ammo drop(if you can manage to get one out of the fucking support guys) and fire away at clusters of enemies. I tried this method using the support class and the burst launcher as well. I found the 320 to be easier.
3rd you need 10 kills inside the metro, that means inside the train station. You can be on the first or second story as far as I can tell.
After you unlock the f2000, bask in its glory.
Note* I used 64 man Conquest for this challenge, to make sure you play a full game of metro join Caspian border first, metro is the next in the rotation. Good luck.