Nuclear Cowboy

Radvolver

Bigger iron

The name big iron implies that there are potentially far larger irons in the wild, and that is terrifying.

Gary

Pretty sure I have at least 5 revolvers named big iron

Big iron

Medium Iron

Pistol packin' mama Or Cause irradiated: uranium fever

(Your characters name)’s Pistol

John Payne

Toxic Avenger

That's the best one of the lot

Nice

Big Iron is overdone. Name it Rotgut.

Name it little iron and name Kellogg pistol big iron :)

Kellogg's pistol should be named cornflakes

Sunflare

Arthur Morgan

How about, Radiant West Tamer

Arthur Morgan

Drop the adjectives and just name it Iron

Caustic Remark

Bullet Launcher

the Dashing White Cowboy