Board Thread:Questions and Answers/@comment-26196925-20160102095932/@comment-25669516-20160104040757

Use the Fast Fire glitch on Demon Thrower. While pressing the shoot button quickly tap the aim button again and again. Upgrade your ammo first so that you don't spend a lot of time reloading.

However since you're still not playing multiplayer its better if you don't upgrade Demon Thrower yet. It's much more useful in Multiplayer than Single Player.