Bar Brawling is a set of skirmish rules for wild west barroom brawls.
Black West is a simple set of free wargames rules for skirmishes in the Old West.
De Bellis Indica is a DBA variant for warfare in India in the 18th and 19th Centuries.
Here’s a Horse and Musket DBA Variant — primarily for Napoleonic and Seven Years War, but since the basic principles of war in that era covered a huge number of conflicts, you could adjust as needed.
From Vae Victis magazine, a DBA variant for the Napoleonic, Mexican-American, American Civil War and Franco-Prussian conflicts.