Showdown (2005)

From the book:

This amazing supplement provides rules for any roleplaying or tabletop simulation of a Wild West shootout, and is both incredibly realistic and easy to use. As well as including a special Shot Clock combat simulator and Silhouette for fast and accurate shooting - where even a near miss can be deadly - Aces & Eights: Showdown provides both basic and advanced fighting and brawling rules. Whether you prefer a quick duel in the streets or a massive gun battle raging through town, this is one western book you can't afford to miss!