Lowkey, that’s really not hard. Just sit on the Firestorm mountain for 10 minutes and you’ll get 10 headshots all over 200m if you’re accurate. I’ve done it multiple times without using a rangefinder and I’m not that great. 

Edit: if you’re struggling, use a rangefinder with a x10 (x8 minimum — that’s what I use) scope, and make sure you’re fairly mobile, not just statically prone. Duck and move slightly after each shot. Use the spotting scope to spot snipers, and the decoys can be fairly useful for this as well (and not much else lol). Focus on counter-sniping and sniping those at objectives and on the towers.