This guide works as of (April 4th, 2016) and takes the updates and playlist changes into consideration.
(THIS IS A BOOSTING GUIDE)
(WARNING) - You can get a CT ban for 2 days or 2 weeks for Idle controllers or not getting a single kill. I suggest all players have the (Make It Rain) achievement so CT bans won't matter.
(PLAYER REQUIRED) (10 players) or (3 with multiple controllers)
(DOWNLOADABLE CONTENT NEEDED) Anniversary Map Pack
(PLAYLIST) ~Team Snipers~
(Step 1) Everyone group up and pick ~Team Snipers~ playlist having 8 spots filled means no randoms
(Edited) (Step 2) Pick (Snipers) (DO NOT PICK Sniper Pro) on *(Breakneck) AKA (Headlong)* or *Ridgeline* If they don't show up vote to skip maps, If it still don't show up quit or play any map then after the game ends you get a chance to pick a map again repeat until you find the maps.
- Mobius Evalon commented which lead me to do more research about this step.
(Step 3) Run players on one team out in the open then have the players on the other team run them over with mongooses (which can be tricky) until they all get the Achievement. Then have the players on the other team do the same.
(EXTRA) Deleting Noble Map Pack and Defiant Map Pack will increase the chance of getting Anniversary Maps.