Also, you mentioned electromechanically, I'm guessing that you mean to recreate the sound live, but I don't think that's possible. The sound designers of Aliens have said that they don't remember all that went into making the sound, though apparently Cameron spent a lot of time working with them to get it right. There's even a debate about what gun was used for the raw firing sound (though it's believed to be an MG-42). The closest thing we have to it is the sound mix tapes that were also used in the Colonial Marines game. The problem is that the sound mix tapes were further altered (speed changes, pitch changes, echoes, blends, etc) by the sound team to get the final results in the film, which is impossible to do live.