The Jackson Gamers have a page with everything you need to know to start gaming Civil War Ironclads
Rules: American Civil War
Fine Tuning Fire and Fury
Here are a set of house rules for “fine tuning” Fire and Fury, the great American Civil War rules set.
I’m not sure I’m on board with all of these.
Honor and Glory Civil War Rules
Honor and Glory is a set of rules for the American Civil War for games where the smallest tactical unit is a regiment, which is represented by four bases. It’s playable in nearly all figure scales. Originally available on the Yahoo Groups, I have archived the files there because Yahoo Groups is shutting down.
Sandpit Showdown: Wild West and Civil War Rules
Sandpit Showdown is a set of free wargames rules for backyard battles with army men in the Wild West and Civil War.
Design and Fight A Civil War Ironclad
Pete Pellegrino has written a set of free miniature wargames rules called Damn The Torpedos. In the game, you customize your ironclad, and then take it out to fight in the Cvil War battle of Mobile Bay.