The Pickett's Charge rule set includes a scenario for the Sunken Lane part of the Antietam battle of 1862, it has roughly 17 regiments and a couple of artillery batteries per side.
I have just put this on the table, to explore the rules as a holistic whole. At 5 brigades per side, this is also ideal Black Powder territory. So far, I am finding a very engaging game, though strip away some of the period terminology and I am feeling that Black Powder might closely do a very similar thing, they are just dressed up differently.
At the moment a powerful Union centre is pressing the Confederate line, but they have taken very heavy losses, but have also put the Confederate line under strain. Things are tight and the next couple of turns will tell. It would certainly be interesting to either re-run the whole game or even just this middle section with Black Powder, just to see whether the game delivers both sides to the same tense and uncertain point.