During the final chase scene between Riggs and Joshua, Riggs
is carrying an HK MP5 submachine gun while Joshua has a CAR-15/M-4 type rifle. In this scene, both weapons have the same firing sound effect, which is not the case in real life as the CAR-15/M-4 has a lower cyclic rate and fires a different round.
When Riggs jumps off the building after handcuffing himself to the jumper, a close up shot just after they step off the ledge shows that the rubber trick handcuffs break. When they get out of the air bag, they have connected real handcuffs on.
When Murtaugh challenges Riggs to shoot himself (after the jumper scene), Riggs cocks the revolver before pointing it at his head. While they are staring each other out, the camera cuts to a close-up of a revolver which shows the hammer moving through half-cock by pulling on the trigger.
While Riggs and Murtaugh are driving to question Amanda Hunsacker's pimp, Riggs lights a cigarette and Murtaugh complains about it. Riggs offers to open a window, but the passenger side window was already shown open in the previous scene.
In the shooting range, Murtaugh clips a new silhouette in the movable target. It is crooked in the clamp. After Murtaugh takes his single shot, and holds the button to bring the target in again, the silhouette is straight.
While in the shooting range, the light on the wall faces in different directions depending on which way the camera is facing. When the camera faces the targets, the light faces the targets. When the camera shifts to Riggs, the light faces away from the targets.
When Martin and Roger go to the shooting range, we see them walking behind the other shooting officers and arrive at their assigned booth, all the while discussing the merits of the case they are working on. While working out their theory, Martin begins shooting at his target, firing a total of 9 shots over the course of the conversation. However, after he fires his last round, he remotely brings in his target, where we see 15 bullet holes.
In The Director's Cut, during the sniper scene, Riggs is seen preparing his Beretta 92 for the confrontation by pulling the slide back and engaging the hammer. This weapon automatically engages the hammer when the slide is pulled back unless the de-cocking safety is engaged. However, after racking the slide, Riggs is seen clearly engaging the hammer after pulling the slide while walking up the schoolyard stairs. Then, right before Riggs says, "I'm still here, asshole. Or, do you only do kids?" he manually engages the hammer again -which would have already been engaged when he pulled the slide back and manually engaging the hammer.
2 of Rianne's girlfriends (one with long hair and one with short hair) come at the beginning of the movie to walk with her to school but when Rianne comes down stairs she is only seen walking with her friend with the short hair to which her friend with the long hair is mysteriously missing.
In an early scene with Roger driving (post hot-dog), the steering wheel is noticeably turned - you can see one wheel pillar and the bolt on the back of it. In the next shot, the wheel is properly aligned. He is not turning the car in either shot.
When Murtaugh and Riggs arrive in the desert, supposedly at sunrise, to get Rianne back, the 'copter and the white limo are filmed at sunrise or sunset, low low sun. When the 'copter lands a few seconds later it is noon, sun at 60 degrees.
When Riggs contemplates suicide and decides against it, he throws his Beretta to his side on the couch. Yet in the next shot where the photo frame of himself and his wife is shown from his point of view, he's holding the Beretta in his right hand. This point of view shot appears to be the same one shown previously before he brought the gun to his head while mourning his wife's death, that was simply re-used.
In the desert scene while Murtaugh is threatening everyone with a grenade, he gets shot in the left shoulder. He still manages to throw the grenade and duck behind the station wagon while covering the wound with his right hand. However, for the rest of the film he runs around in a white tank top T shirt and shows no apparent shoulder wound from being shot earlier in the day.
When Riggs gets shot by Joshua and flies through the storefront window, it's pouring rain outside, Murtaugh immediately runs up to make sure he's okay and they walk a few feet to their car and suddenly it's clear out without a drop of rain coming down with the exception of the rain drops on the cars windshield. When they start driving back to Murtaugh's house, the rain on the windshield is gone, and the road is now dry. The roads remains dry until the car turns onto Murtaugh's street, when they're all of a sudden wet again.
Joshua shoots open the front door of Murtaugh's house and walks into the kitchen. The TV is turned on and the breakfast table has a two cereal boxes, some flowers and some place settings on it. It is being lit by the light hanging above the table. Joshua fires a couple of shots into the TV screen to turn it off, and when it cuts to a wide shot with Joshua's back to the camera, we can now see that the table is covered in debris and the hanging light is out and laying on top of the table even though he never fires his gun at that area of the room.
After Riggs flies through the store window after being shot by Mr. Joshua, Murtaugh helps him to walk back to the car. It's obvious that they're parked in front of a knitting store with a big front window and a small awning over the doorway that says "knitting-needlepoint." A few seconds later they jump in the car to leave and they're suddenly parked in front of a Jaguar dealership.
In the opening scene of Amanda jumping to her death, the stunt woman was actually filmed falling onto a tarp that had been printed with a photo of the cars. Just as she hits, the tarp can be seen stretching and wrinkling with the impact.
In the Director's Cut, Riggs reports on the police car radio that he is on the way to the sniper call. The next scene draws away from the car showing Riggs en route to the scene. The antenna holes in the roof & trunk are filled with rubber plugs. This is standard for decommissioned police cars after the police radios & antennas are removed.
In the beginning of the movie when Riggs is attempting suicide he removes the magazine and chambered round then places his "hollow point" in the chamber and closes the slide which would have cocked the hammer however as he is struggling with the decision to shot himself you see him cocking the hammer.
In the scene with Dixie's house exploding, you can see the yellow prop sticker on Riggs' gun. When they walk to the car right after the explosion and later when Dixie's body is being taken out.
That is not a prop sticker its the gold Beretta emblem on the grips . The early 92F were issued with grips with a gold Beretta emblem on both sides. They were later changed to all black grips.
When Riggs is being tortured by Endo and Joshua, he is supposedly swinging suspended from a hook, and must later pull himself up to get free. But in the wider shots, you can see his knees bent; his feet are already on the ground, and all he would have to do is stand up (or on the edge of the trough at his feet) to lift off of the hook.
When Riggs and Murtaugh shoot Joshua after he overpowers the cops trying to arrest him, the slide (top half of an automatic pistol that moves backward when the gun is fired) on Riggs' Beretta doesn't move.
When McAllister's car is flipped by the bus, the hole in the floorboard for shooting out the section of telephone pole used to flip the car can be seen. The section of pole can be seen rolling down the street as the car is flipping over.
In the Director's Cut of the film, Riggs loads his Beretta before going to work. He is seen loading the magazine into the Beretta and racking the slide. The slide sticks as he pulls it back, indicating he is actually loading an empty magazine.
In the Director's Cut DVD, the scene in which Riggs bravely puts himself into the line of fire of a sniper shooting at kids in a school yard, you can see Mel Gibson sneaking a look down at the pavement to find his mark as he's walking forward before shooting the sniper. After he's shot the sniper and bends over to pick up his empty clip, the mark can be briefly seen on the bottom of the screen.
When the bus hits the General in his getaway car, in one shot you can see the car flip after a small explosion propels it into the air, while the bus continues to roll through the supposed impact point with no damage to its front end or windshield and the driver (possibly a mannequin) sits absolutely still in the driver's seat, but in other shots the bus stops abruptly on impact while the driver bounces around.
Obvious stunt performers for the explosion: when Riggs and Murtaugh start walking across the street to the hooker's house, Murtaugh is taller than Riggs. In the next shot showing them from the back, just before the explosion, Riggs is taller than Murtaugh.
When Riggs, Murtaugh and Rianne exit the club after the shootout in pursuit of Joshua, he shoots back at Riggs, blowing out a tire on a parked car. Lots of flame and sparks inside the wing indicate the tire is destroyed by an explosive.