Civil War tactics: Bloodiest in history? Really?

I am, with the help of a couple of hundred friends, working on a book for Civil War reenactors. What promises to be the main chapter is called, for now, "Interpretive Myths, Mistakes and Misunderstandings."  It's a compilation of all the wrong things reenactors tell the public when "interpreting" history for them.
One of the biggest myths is probably going to be the alleged deadliness of Civil War battles, the one that says armies continued to use Napoleonic tactics despite the introduction to the battlefield of new rifle muskets that more than tripled the range at which accurate fire could be put down.  It's very popular and has many of the hallmarks of what we today call "urban legend."  This one gains strength from the ironic juxtaposition of humans smart enough to build a better weapon but not smart enough to adapt battlefield tactics.
There's a couple of points the chapter will explore, including whether a more accurate weapon in the hands of a poorly trained shooter is really more effective and whether tactics had in fact changed to accommodate a variety of new weapons with new capabilities.  (Short answer: Of course tactics changed.)
But the "killer facts" appear to be these:  The percentage of killed and wounded in the American Civil War is about the same as during the Napoleonic Wars half a century and more earlier.
Others have done studies based on the number of cartridges consumed at a battle. They've come up with numbers that say, for instance, something like 400 shots had to be fired in a Civil War battle before one of them hit the enemy. There's no reason to doubt the overall truth of those numbers: Tracking ammunition use was a standard procedure and the numbers are probably consistent, if not 100 percent accurate.  But what does it actually mean? And how does it stack up against Napoleonic times? A lot of the ammunition consumption stats I've seen so far for Napoleonic battles appear to be rough guesses. I'm still sorting that out.
It seems like there ought to be a better measure. I'm going with "percentage of killed and wounded of those engaged."  Those numbers are also reliably consistent, in both eras.  It was one of the "scorecards" used to keep track of how the wars were going; it always has been.
The research is tedious. It is frustrating to realize just how many battles there were in Napoleon's time and how many there were during the four years of the Civil War. And not all of them are easily compared: How do you deal with a three-day battle like Gettysburg, where some units were engaged more than once? And how many do you need to stack up and analyze before you're sure you're not just happening upon the ones that support one position on the question? What's a fair sampling, in other words?
The research is of course incomplete. Analysis so far of easily deployed battle numbers shows, though, that reenactors are probably overstating the bloodiness, at least compared to the Napoleonic era. Waterloo, for instance: 190,000 engaged on both sides, 55,600 killed and wounded, 29.3 percent "bloodiness ratio." We can compare it to an equally important and, generally, equally significant battle where everything was on the line for both sides: Gettysburg. There were 165,620 engaged, 35,087 killed and wounded, bloodiness ratio of 21.1 percent. 
Clearly this one is going to upset some folks who cherish the myth the way they like to tell it.