At 9 Min and 30 sec. when the soldier is walking away. A helmet appears and starts rolling on the ground. There is no helmet when he is running up the the soldier after the fire fight and nothing while he is walking away. Just a helmet appears out of thin air.
When Taliban are shooting from the mountains during various scenes in the movie, the muzzle flashes are clearly visible, which in reality should be nearly impossible to see in broad daylight.
Two of the vehicle positions are referenced as LRAS 1 and LRAS 2. An LRAS is a Long Range Scout Sight System (LRAS3), a very large, boxy sighting system found in light scout units (like B/3-61 CAV). However, none of the gun trucks have this system, as it is mounted next to the cupola weapon system.
When SSG Romesha is using the machine gun on the generator, and it is hit by the RPG, it would not leap as shown - the commercial generators are extremely heavy and an RPG warhead only has a few pounds of explosives.
Early in the film, Captain Keating summarily reduces Faulkner to Private for smoking hashish while on duty. In reality, a reduction in rank can only occur via a process called an Article 15, which is essentially a hearing where the accused Soldier has an opportunity to present evidence and arguments in his defense. In reality, the process can take several days.
When SPC Carter delivers ammo to LRAS2, he claims he brought 5.65 in the magazines he hands to SGT Gallegos. In reality, the ammo caliber is 5.56.
The quick reaction force arriving to relieve the base is surprisingly lightly equipped. They are not carrying magazine pouches or canteens which would be important if they were going to fight a battle.
In multiple scenes after characters urinate a "zipping" sound effect can be heard as they refasten their fly. In reality Army Combat Uniform pants have button flies, not zipper flies.
When Carter gets Mace into the vehicle and closes the door, the cameraman is visible on the windows reflection.
The counselor seeing SPC Carter at the end was an Army officer, and should not have been wearing earrings with a field uniform.