This thread is still open?
Pretty much anything can have innuendo if you think about it while suppressing enough brain cells:
Muzzle flash
Lever-action
Pump-action
Muzzle load
Gun case
You know, it's amost pointless to continue this list. I think it would be a shorter list to make of terms that could not be sexualized in any way.
Adjustable night sights?
Specific calibers? (40 S&W, 454 Casull)
Dehumidifiers?