Have wondered what that Tremors graboid popper double rifle was
I used to get irritated at inaccuracies with incorrect/out of place and time prop guns. But not so much anymore. I can't imagine the nightmare it would be to properly outfit ever single movie or TV show to correct time and location for the huge number of props required. Lately I just go with the flow. There are only so many of each possible type of firearm available, no matter how many are in storage or for rent by prop houses. Now if it gets to the point where a pirate, in the the 1700s, pulls out an AR and starts shooting, well I guess I'll have to draw the line! Usually I just let it slide if for example they pull out a percussion caplock pistol when the movie is decent otherwise. Plus why ruin enjoying the fantasy of any movie with trivia of small errors, particularly when it is one of the support cast in a big battle episode. But, for the most part, most directors and producers seem pretty good about matching their prop firearms to time and place. It seems most of the time they make an honest effort to do so.
One of the most obvious errors was likely a design "have to". It was the Winchester Model 1892 loop lever used in the very popular Rifleman TV series. It was modified with a small set screw added by the show's armorer/gunsmith. The set screw was in the trigger bow and contacted the tip of the trigger just as the action closed. This allowed for the fast rate of fire of the loop lever M92 44-40 used in the show. The only problem with using an M92 is the show's setting is in SW New Mexico in +/- 1887. The correct rifle or carbine of that era would have been the Win M1873 but the producer and armorer, IIRC, decided the '73 simply wasn't as suitable for the modification as was the '92 and the audience either wouldn't know or care much if it was a little out of the correct time setting.
I get a kick out of seeing or noticing jams and off-synch report noise to shots and smoke. Seems to happen most often in larger battle scenes with many supporting actors firing this, that or the other type guns. In the African Queen, some of the German Army's local conscripts manning the fort on the river are shown really fighting with and jamming some of their bolt actions as they are shooting at the African Queen as she chugs by.
Some non-firearm props on shows/movies are also real head scratchers. Recently I was watching an old episode of Dr Who, obviously filmed on a stage set in England. There was a neck/shoulder mount of an NA Pronghorn on the wall of the house or apt. How in the world did the prop house in England, supplying the show, end up with a pronghorn in inventory and why did the director use it? Made me chuckle and wonder anyway