I just started killstreaking the other day and the way i do it is get into a demolition team tact with 8 friends or 12 people demolition and one person stays on the bomb constanly planting/defusing in turn your dier doing the same thing to keep the time going..average game last about 1hr. and about 800 kills hope this help you...if you know any other ways to make the game last longer and get more kills let me know please..and im also need help explaing how to lock the lobby because some people are dumb and back out during the game and messes it up for everybody so if you could it would be very much appreciated