This should be easily achieved if you are going for all the weapon kills. just always make sure to be aiming at the persons head. every stock gun can easily get headshots and even melee kills (B) aimed at the head count aswell. This should come naturally after your 3rd game of boosting weapon cheevies. Here is my strategy to boosting the weapon achievements. And as i said, just keep aiming for the head while following my guide!
I suggest boosting this with 4 players as it goes by much quicker. Start a deathmatch on Campus with running speed set to 1.5x, points to win at 0 and time limit 30minutes. Have everyone start with the same weapon then run to the central area right in the middle with the low roof and one wall being windows. Each person take turns getting 50 kills against the other 3. The three dying just keep lining up against the wall opposite of the current killer and rack up the kills. Since everyone should be spawning with the same weapon, no issues with running out of ammo should occur. just pick up the fallen's ammo right in front of you. All 4 players will have no problem getting 60 kills or more in one 30 minute match. this has been tested and proven effective
Keep getting those head shots!