Author Earl Hess argues in a new book that "the heavy reliance on earthworks by both armies in the Overland campaign was driven by Grant's relentless attacks against Lee, not by the widespread use of rifle muskets, as historians have previously argued." (This quote is the publisher's paraphrase of Hess's point.)
Whatever the merits of the first part of this hypothesis, I am very persuaded by Nosworthy that the Civil War was the last great musket war.
(More Nosworthy here.)