MGR is a specific general item upgrade setup that wipes away zombies in a large cone, allowing you to save yourself in a sticky situation.

Buy or start with the revolver pistol, obtain the weapon mods split, grow, and spread shot. Then, make your fire rate higher, you do not need max, just at least halfway. And, that's basically it, you have a fast firing, shotgun style, enlarging bullet revolver.

Instead, you could use heavy rounds and two spread shots to make a slower, harder hitting, wide blast, that makes bosses pretty easy.