This trophy requires you to fulfill three requirements.
Select the Assault SA+ kit and scroll down till you see the gold coloured M16 gun.
A good way to grab these pins all in one game is to find a boosting partner load up a game of Squad Rush on Cold War map with Hardcore mode turned off. Inform your partner once you've loaded into the game and let them search for you and they will be placed on the other team.
Blow up Objective A after this have your partner run towards you (as they have unlimited lives for being on the defence team) and just kill them a 100 times.
After 5 consecutive kills you will unlock the "M16 SPECACT Efficiency Pin"
After 8 kills overall you will unlock the "SPECACT Assault Excellence Pin"
After 100 overall kills you will unlock the trophy "SPECACT Assault Elite"
Repeat this process for other trophies for the kit upgrades.
You can get these in normal gameplay please note these trophies DO NOT unlock in Onslaught Mode.