Boosting these kills with 4 people makes the process go much faster. If you have been going for all weapon kills then once you have earned 50 kills for the N6A3, AT-S, M77, thats 150 right there. you can use any of the three weapons already used for the final 50.
The quickest way I have found is to use the M77 remote grenades on Rubble during a capture the flag game. set the game to 30min, 1 capture to win, and then 2 v 2. three M77's spawn on top of each base. Run to enemy base and have the people dying go to the back corner to the left near where the grenades spawn. Just keep throwing M77's from the balcony of enemy base and killing them there and the guys will keep spawning in that corner over and over. very quick process. all four boosters can easily get at least 50 kills in 30minutes. Can do this for NA63 kills aswell since they spawn in the same corner you are boosting in.