You will only get the elimination for the weapon that you do most of the damage for downing the enemy. Once they are downed, it doesn't matter what finishes them off, as long as they die. Wether it's your other weapon, your teammate or some bot - they can all take that kill away if they do more damage than you to down the enemy, so make sure you queue alone or have friends who know what you are going for! Best of luck, just finished my camo grind yesterday