One thing is that when the troops were given their guns, they were rifles as opposed to muskets--rifles were better because they were "rifled" and had small grooves on the inside of the barrel, which made them much more accurate. However, they were not widely used during the Civil War yet; mainly they just fought with single-shot muskets. It was uncommon to find an entire regiment armed with rifles, and an all black regiment certainly wouldn't have had them.
try this one:
http://www.imdb.com/title/tt0097441/goofs
Three more links you might find helpful. The first two are invaluable resources for specific historical inaccuracies (at least, they seem to be at first perusal). Good luck!
http://www.mtholyoke.edu/courses/rschwart/clio/morgan_glory.htm