No, you are not suffering from the Mandela effect if you saw “Aliens” in the theater in 1986 and remember a really cool scene with some automatic remote sentry guns placed in a corridor — against which waves and waves of monsters launched an attack.  And you aren’t insane either.

The scene was in the movie when it originally played in theaters, according to my sources on Reddit and Youtube.  But it was not included on the VHS version (whether it’s referred to the “theatrical cut” or not). 

Variations of the scene can be found in different subsequent cuts of the film, according to fans online — like the director’s cut or the special edition, or versions appearing on television. 

Some include dialogue we remember from 1986.  (“Next time they just walk right in,” or something like that.)  And at least one includes the shots of the aliens being cut to pieces in the corridor.  (Notably, the scene below does not.)

Anyway, I am linking to the totally awesome Alien Fire Team Elite on Youtube for the video.  Semper fi, gentlemen.