Factual error: The film is based during the Battle of the Bulge which took place from December 16th 1944 to January 25th 1945. However throughout the entire film the area appears to be mid-summer. No snow in sight. (00:07:50)
Factual error: Declan takes a gun from his glove compartment and nothing else. I counted that he fired 22 shots before being put down. There is no way that gun had a 22+ round magazine.
Factual error: When Joseph Gordon-Levitt is playing poker, they are using Morgan style silver dollars. The stacks of dollars are treated as $100 dollars. But a Morgan dollar is 2.4 mm thick, a hundred dollars would be 9 .44 inches high and the stacks of coins were about half of that. (00:11:00 - 00:12:00)