.50 calibre rounds from a heavy machine gun are shown bouncing off the front of an unarmoured jeep. In reality these rounds would easily penetrate the engine and destroy the vehicle.
When Carol changes out the empty magazine on the M-4 she takes from one of the dead Saviors she is showing firing on the other Saviors without cocking the rifle with the charging handle, this needs to be done when reloading a empty rifle in order to chamber a round.
Yago, the Savior Carol tried to "negotiate" with, is carrying a Ruger Mini-14, which is a semi-automatic rifle. Yet the rifle is shown being fired in full auto.
Throughout the firefights, it's obvious they aren't even using blank ammunition as the rifles actions are not reciprocating and no brass is being ejected. They are however adding muzzle flash, which is impossible with rifles that aren't functioning.
When Jerry and the King are at the gate, they are only a couple dozen feet from the heavy battle Carol is waging in the parking lot, yet no gunfire is heard and Jerry and the King never notice all the shooting.
During the standoff in the parking lot when the two Saviors are crouched behind the front of the HMMW-V, Carol could simply shoot them in the legs under HMMW-V which has especially high ground clearance.
If Carol had not hesitated when she arrived at the parking lot, she could have killed all the Saviors while they were distracted loading the machine guns into the HMMW-V. Instead, she waited until they were unoccupied and until after they broke into two groups. This was much more dangerous as the second group provided overwatch which endangered her and made her battle much more difficult.
When Carol takes a hostage, her head was very exposed to the Saviors so they could have attempted shooting her in the head. This may have been a dangerous shot with a handgun, but a rifle is extremely accurate especially at such a close range so shooting her should not have been a problem. Although risky, they ultimately killed their comrade to get to Carol, so it would have been worth taking the shot.