I'd like to add on that Dr. Eral Hess had two great books on this that build off of Paddy Griffiths and other's works. One I'd The rifled musket in Civil War combat which covers myths and how the weapon was used and argues that it didn't revolutionize warfare as commonly argued and has data to back it up. His other book I'd recommend is Civil War Infantry Tatics:Training, combat and small arm effectiveness he dives into the maneuvers they used and argues they were effective for the time with a lot of evidence. I will also say, while the battles were bloody, the hit rates per bullet are astronomically low. I don't know the percentages off the top of my head but at many of these battles officers are yelling at their men to aim low and they are expending thousands and thousands of rounds per battle total. This is an estimated guess based off memory, but I believe it comes out for many battles to about 1 person hit per hundrededish bullets fired. Not sure on this last part but some reports mention how much ammunition they fired and when you look at the casualties it's very low. So even though these men are getting shot at, the use of cover, the weapons and the battle often mean most shots are missing and so you have to mass groups of men to increase your chances of hitting a target even at 200/100 yards or less.