Shotgun Farmers

Server settings:
Create room:
Free for All: for mode
Time Limit: 10
Max Players: 10
Allow bots: on
Maps: Any

Go to the right hand side and select these GMO's
Random Weapon: This will spawn you and everyone else with a random weapon, increasing your odds of spawning with or finding ammo for this gun
Fertile Fields: This will massively increase the rate at which crops grow drastically increasing the ammo you will find for special weapons
Big Heads: This will make headshots way easier for much faster kills and easier 1 hit kills with sniper type weapons

Try to aim for the ground around your opponents as opposed to the opponent itself as it has a large explosive radius and is much easier to hit them this way.