Yeah Biggiesmalls is more or less right there
Go into Ground War your partner joins your sessions hope your on opposite teams if not only ONE of you leave quickly then re-join because it sometime changes the teams about and then you find a hiding spot and kill till you get AC130 then you put tac Insert down die and kill your partner again do this 3x then call in all 3 AC130's one after another

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Best ways of doing it is on Domination on bigger more open maps like Derailed, Wasteland, Estate ect. Domination only because TDM has really bad spawning....e.g. all your team or your partners team spawn right next to you and you end up getting killed because they notice you when they spawn.
if you are having trouble on Ground War try normal domination just mean you get less kills but can be a little easier than ground war

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Hope this helps if it does +Rep please