Boosting method: Grab a friend and both queue up for a solo match in the same region and make sure cross platform play is set to disabled. Have one person count down to queue up at the same time and meet up at by the driver to ensure you both got into the same match. If you are having trouble maybe try a server that isn’t as busy at the time. Next you will want to head to around D2 on the map and both get a gun. Slug rifle and revolver are preferable but the burst rifle will do in a pinch. There are better weapons, but you don’t really need anything fancy for boosting.
Using the picture below, have one player on the highlighted rock and the other on the road where the horse is. Now just trade a knock and the achievement should unlock in game. If you didn’t get it have the player on the road move further back. You could do this at other locations but this has a nice open sight line and typically has very few opponents nearby.
The required distance is around 2/3 of a square on the map.
Regular method: The Assassin class sniper rifle or the Hunter class longbow have high damage with accuracy and high bullet velocity making these the best weapons for this. Alternatively you could use a high quality slug rifle but it isn’t quite as good. Once you have one of these head to a mountain, hill or tower with a long sight line and wait for someone to target. Remember you only have to turn them into a chicken not finish them off.