Continuity mistake: After Chamberlain's bayonette charge, he sees his aide wounded for a second time. The scene changes angles back and forth during their talking of how brave the boys were. An American flag is over the shoulder of the aide on close ups, but on a longer shot the flag is leaning against the tree.
Continuity mistake: During the sequence at Little Round Top, the same footage is used twice. The 20th Maine soldiers discharge a volley of musketry and there is a shot of a Confederate soldier being bodily flung backwards. A short time later, the Union defenders send down another volley and we see a close-up of another Confederate falling. Only it's the same actor, same footage, from a different camera about 35 feet down the Union line.
Continuity mistake: At the beginning of the movie when the scout is talking with Longstreet, when the scout holds up his finger and says "you didn't know they were on the move out there", a long stream of troops is seen marching to the right. When the shot cuts to Longstreet then back, they have disappeared.
Continuity mistake: At the beginning of the movie it is dawn of June 30th, but should be dawn of 29th. Harrison the scout completes his task and reports to Gen Longstreet. Longstreet confers with Lee and it is now evening. The next several scenes show a new dawn when Sorrell asks if he should wake the men, Buster wakes up Col Chamberlain and a bit later Gen Buford arrives in town with his cavalry and no fighting yet. This second dawn should be June 30th, not July 1st, the first day of the battle. Further that day ends with Buford drafting report for Gen Reynolds.