For 90% of the Joe Schmoes that have that muzzle device and don't know what it's for I would have to agree with you. However it does have a purpose which is breaching. The teeth dig into a wooden door frame a little and keep it from moving and the length spaces the muzzle away from the door and lets gas escape through the vents. It's for breachers. Saying it's "Gay" or "French" is just showing ignorance.
To the OP I'll buy the shit out of one of those mounts if it comes out for an 870.
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