Factual error: When Col. Yin threatens to execute Cpl. Opelka, he draws a semi-automatic handgun, racks the slide and hands it to a subordinate. The subordinate puts the gun to Opelka's head and pulls the trigger but nothing happens because the pistol isn't loaded. He racks the slide again and puts the pistol back to Opelka's head and Opelka looks terrified as again the trigger is pulled and nothing happens. This is a mistake because if there were a round in the magazine the first time the slide was cycled it would have been chambered. If the weapon wasn't loaded the first time it was cycled, they could have cycled it all day long and it wasn't going to chamber a round. And a Special Forces soldier like Opelka would have known that.
Factual error: Almost throughout the whole movie, US soldiers wear full on camouflage. The army didn't wear camouflage in Vietnam, they only wore solid green uniforms.