The wizard there among them had a big iron on his hip...
( Gun inspired by the classic Marty Robbins song: https://youtu.be/-NuX79Ud8zI )

Custom Wand: The Big Iron

An ancient revolver made to launch heavy projectiles while controlling their recoil. Can be fired very quickly if its six spell slots are loaded with lighter spells.

Custom Spell: Magnum Rounds

The most powerful handgun round in the world. Devastating at point-blank range, with the consistent velocity needed to reach distant targets. Pairs well with a spread-reducing wand.

Note: Adding magnum rounds to more than one of the big iron's spell slots does not affect fire rate or reloading. However, other magic spells may be effectively burst-fired with it.

Loot Ammo

Raid the lockers and footlockers found in army bases to get more/larger boxes of bullets to distribute among your six-shooter and other wands.

Thanks to Eman for the wand template I started with, as well as to ryyst, Coxas, Horscht, Zatherz, and others from the Noita Discord's modding community!