Speaking of the Ironclads, here's a good site concerning the Civil War naval subjects.
http://www.civilwarhome.com/navalwar.htm
Dahlgren guns were, IIRC, breech-loaded rifled guns. All large caliber naval guns have always been "single-shots" - manually loaded for each shot. Even at the end of the Battleship Era - the Iowa-class ships still were loaded manually.
Imagine if Teddy and his Rough Riders had been equipped with the AK, instead of the then-obsolete Krags against the Spanish Mausers. That hill would've fallen all the more quickly.
Or perhaps the militia in Concord, facing the Brits with AKs in their hands. We'd have soon owned London.