Triggered calling card

Hello everybody, I´ve been struggeling for days with this one. Earn 3 rigged medals. From what i learned online your only real ways are C4, blast traps and Spring. I treid hardcore and core for this one. But whenever im lucky enough that 2 people are on a flag or hardpoint at least one of them plays flak jacket. I also think C4 which is probably the best bet is quite week. Any tips with this?