I don't have the BP rules, but I've seen this discussed before on other forums and the consensus among dedicated Civil War players seems to be that BP is too generic for the ACW and lacks period flavor/detail. What exactly is missing, I couldn't precisely say. And of course, if you don't know either, you'll never miss it
Personally I would wait until they do a dedicated ACW supplement.
For skirmish gaming in 28mm, I've played
Terrible Sharp Sword and really enjoyed it and I also think
Bull Run to Gettysburg looks good, which I have read but yet to play. I believe that Architects of War are coming out with a set called
Uncivil War or some such with should be similar to
Muskets and Tomahawks for skirmish gaming as well...