Can Be Done Across Multiple Playthroughs/ Rounds.
Use Either The Ballistas Or Catapults.
Ballista -
+One Hit Kills,
- Can Be Blocked By A Shield
~ Medium Reload Time
Catapult -
+Hits Large Area With Massive Damage
- Teammates Will Die
- Takes Two People To Operate Effectively
~Medium To Long Reload Time (Depending On Aim Distance)
Either Can Be Broken With Swords, and Fixed By Holding Down The Use Button.
Get 50 Kills And The Achievement Pops.
Goodluck!