David Wareham offers a set of free wargames rules for the 19th Century along with army lists. Scale is 1 figure to 30 men.
Rules: 19th Century
La Petite Guerre Skirmish Rules
La Petit Guerre is a set of free wargames rules for small scale actions in North America in the 17th – 19th century.
Fire and Fury America’s Wars
I think Fire and Fury is the finest set of miniatures rules ever written. It has elegantly simple mechanics, fun gameplay and set the standard for high-quality rules presentation.
Now the Fire and Fury people are at work on a version for America’s other “horse and musket” wars: The Revolution, War of 1812, and Mexican War. You can find the playtest versions of Fire and Fury: Americas Wars here.
Most Irregular Horse and Musket Rules
Most Irregular is horse and musket rules extension to the Fast and Dirty skirmish rules, found on the same page.
Gold Rush Mounties Rules
Gold Rush is a set of free wargames rules for late 19th century action in the Yukon.