A screen weapon has a physical production identity and a fictional identity. The real object used to make a prop need not share the name, specification or history assigned to it in the story.
Physical object and fictional design
The Aliens pulse rifle used a .45-calibre M1 Thompson as its underlying firearm. The weapon presented within the fiction is a different design with its own specification. Describing the production object therefore requires a different answer from describing the weapon carried by the fictional Marines.
Star Wars provides another example: the E-11 blaster design drew on the British Sterling submachine gun. The visible relationship supports a production history, not the existence of the blaster’s fictional operating technology.
Different objects for different shots
A character’s single weapon need not correspond to one physical object throughout production. Lightweight solid pulse-rifle versions were made for stunt use alongside heavier props.
The production requirement changes with the shot. An object photographed for detail and an object carried through physical action need not have identical internal construction. Their common task is to represent the same fictional item at the level visible in the finished sequence.
Later alterations
The Royal Armouries pulse rifle was rebuilt for Alien 3 and later repainted. Its museum condition therefore belongs to a history extending beyond the original film.
A present-day photograph of a prop cannot automatically establish its configuration in an earlier shot. The relevant comparison is between the identified production version and the screen image being discussed.
What remains continuous is the represented weapon’s identity within the story. What can change is the underlying object, the physical version selected for a shot and the object’s condition after production. Keeping those layers separate explains both recognizable real-world ancestry and departures from it.