Ross MacFarlane offers a set of set of free wargames rules for the late 19th/ early 20th centuries called Sending MacDuff to the Front.
Volley Fire is a set of 2mm wargames rules,
designed for lots of volley firing infantry with rifles, horse and cannon. It is meant for simplicity, so ignores morale and commanders and such likes, but maintains a certain amount of realism in certain areas. These can be written in at a later time. I’m very open for suggestions. Anyhow, on with the tour!
Each player has an army consisting of several companies of infantry or cavalry, and batteries of artillery. Infantry companies are made up of one to five platoons, cavalry of a similar number of squadrons, each of which is represented by one strip of models. Artillery batteries consist of a similar number of guns. Units can be either Close order (c.o.) or skirmishers.
The Mexican American War Yahoo Group has a set of skirmish rules for that conflict, “in the spirit of the Sword and the Flame.”