**UPDATE** With the latest update, you should be able to search for my fileshare and download the map!
To find other players in MCC, select your name in the Roster, then select "Find Player" to access their file share, etc.
I have set up a Forge map you can load up in custom games and shared it in my file share. It's titled "Headshots" and I'll give you a brief explanation of what to do!
The map is set up to accommodate 16 players, with one person getting headshots at a time.
1. Set the map settings to Slayer(I have a custom Slayer setting also in my file share that you can grab), make sure to turn all respawn times to instant and set player weapons to infinite clip(you might want to set player shields to zero or up the weapon damage but it shouldn't be too necessary).
2. Bring in as many extra controllers as you can!
3. Choose who is getting headshots, and have them grab a sniper and stand on the ramp facing the spawn points. Find the spot where you can stand to get a straight headshot off of all the spawning victims at the same time, then keep pulling the trigger as fast as you can!
4. Enjoy!

If you need clarification, please ask!