Whilst browsing for GiFs I saw this one from the movie Green Slime, the movie which included a spaceship which likely inspired the toy SpaceX LT10. When I saw the space gun I thought - I've seen that before! Its clunky shape reminded me of a toy rifle.
This is it, the rifle shown below in this boxed Gerry Anderson's Starcruiser Mission Kit by Thomas Salter Toys. Now I don't have this toy so I can't be certain of its size. Its sort of similar but not quite the same.
Can anyone do a comparison of the movie rifle and the toy itself if you own one?