There are 14 possible weapons you can use whilst on the mission Old Comrades, and they are listed below:Pistol
At the start of the mission Nikolai will open a brief case containing three different pistols, pick one of them up. You will then head on downstairs and encounter a bunch of enemies. Kill one of them with the pistol you picked up, run over to their body to see if they’ve got a different pistol to the one you are carrying. If not, then don’t worry too much as there’s plenty of weapons to use.
Then head on inside and you will find the MP7
on the table and one of the enemies will be carrying a 1911
and another enemy will sometimes carry the M19
. Continue into the next room and the Model 680
will be on the snooker table. Also, in this room an enemy will usually be carrying the FR 5.6
. Go though the kitchen and the guy on the stairs will have the P90
Head on back outside and you’ll be brought to a road that you have to fight your way down. In this area you can find the FAL
and the AK-47
on some of the enemies. After you’ve jumped out of the window you will encounter some more enemies, check their bodies if you are missing a weapon. You will then head down an alley way with a guy on a high ledge and someone in front of you. Here they can potentially drop the 725
Next area is the final room where there are a few enemies. The last two possible weapons you can use if the M90
which is in the van you have to get into. Pick those weapons up and you should’ve used enough weapons to get the achievement. The achievements pops during the next cutscene.
This achievement isn’t really that difficult on Recruit, only hard part is remembering what you have used as you can’t stay in an area for too long.
If you are still struggling, then feel free to use this as a reference.Call of Duty: Modern Warfare Hot Swap Achievement Guide