Revealing mistake: When the 54th Mass. marches past a liberated plantation some black children wave them on. One of them is wearing a digital wristwatch.
Revealing mistake: Rubber bayonets quiver every time the Federal troops hit the sand for protection during the climactic assault on Fort Wagner. It sort of wrecks the mood.
Answer: To add to the answer, it's shown in the film in this scene as a soldier approaches a pile of shoes and places a pair on the pile and grabs another.