On the 20th anniversary of its original publication, War Artisan's Workshop now offers a digital re-release of Rifle Wars, Part I grand-tactical American Civil War rules. The system is essentially unchanged from the hardcopy edition, but with some light editing for clarity, additional examples and designer's notes, and a few tweaks to allow it to be played with pretty much any basing system.
It comes in two formats – a 32-page full version with color photographs, and a 15-page "Essentials Only" version with just the rules and black-and-white illustrations for easy printing.
See the rules page at warartisan.com for a brief introduction to the rules, including general notes on the rules, the sequence of play and table of contents, and an extended sample combat.