Still waiting for the barrel clamp to arrive so I can finish mounting the sling.
That's a hell of weapon you got there. Doesn't count though, because Uncle Joe said it had to be a double barrel.
It's a choke... "Remington Tactical Choke." Basically a door breacher. I don't like it personally. I think I'm going to swap it out for a regular improved cylinder choke so I can still blast these out of it.
It is made so that you can jam it into a wooden door between the knob and the frame and the teeth dig into the wood. Then you pull the trigger and blow the lock out.
Just go to youtube and search for "shotgun door breach"
I've got the same Remington 870 Magpul with the "door breacher" choke. It's designed to be forced up against the door lock and then let er rip. It's really more of an offensive police type add-on but it came standard with that model 870 Remington with the Magpul features.