Smoothbore guns can be quite accurate at 75 yards. Prof. Lawrence Babits (Devil of a Whipping) scored four out of five hits at 75 yards on a man sized target. He was loading and firing as quick as he could too. One interpreter at Colonial Williamsburg told me that when they benchrested their replica Brown Bess, they consistently struck a man sized target at 100 yards. The trick - everyone practiced. That was not something the soldier of the flintlock era did much of as it was considered a waste of shot and powder.
Vigilantibus et non dormientibus jura subveniunt. Molon Labe!