Goofs

Everyone inside the house hears the gunshots from the barn, yet just a few minutes earlier they didn't hear any of the gunshots from the guardhouse's machine gun. The guardhouse is about the same distance from the house as the barn, and the machine gun in it is a Russian .50 caliber NSV 12.7x109mm, which is far louder than the 12 gauge shotgun Reacher was using in the barn, and would have easily been heard at the house, even over the sound of the music.

A beard trimmer works on fairly low voltage, and doesn't have the power to electrify someone when thrown into water.

Reacher tells Paulie in the last fight, that he plugged the barrel and that is why the M60 blew up, but at no time did Reacher lift the feed cover or stick anything into the barrel and charge the handle during their fight.

Correction: Reacher didn't need to charge the gun, it was already loaded as evidenced by him firing it immediately before plugging the barrel. Just prior to Reacher being knocked into the window his hand can be seen quickly grabbing the muzzle of the gun, which is when he stuff the round into the barrel.

At approximately 3 minutes, Reacher goes to grab a gun that has been dropped on the floor by someone else. However, he visibly fails to pick it up - yet a couple of seconds later it's in his hands and he uses it to shoot another would be assailant.

Correction: Reacher was attacked right as he was about to pick the gun up off the ground, preventing him from picking it up. The gun he winds up using belonged to the assailant, Reacher took it from his attacker just before shooting him with it.

When Reacher confronts Taktarov he comments on the fact that he and his men have many guns, but Reacher is all alone. Then Villanueva approaches saying "not quite" and Taktarov says "okay, so you have two guns" then Duffy walks up and says "three". Both times when Villanueva and Duffy say their lines the sound effect of a hammer being cocked is heard; Villanueva has a Glock 17 and Duffy has a Glock 26. A Glock is a striker-fired pistol, meaning it has no external hammer and can't be manually cocked.

In the opening scene Reacher has a 21st-Tec Bellator sniper rifle, which is bolt action, however he is shown firing it as if it is a semi-automatic. Several times he fires multiple shots without cycling the bolt.