That's just an extended choke tube. Briley makes them along with other manufacturers. The style is the Invector Choke, not to be confused or interchanged with the Invector Plus chokes.
FN even has a custom set.
They are nice b/c you don't have to have a wrench to install and remove, just remember to give them a twist just before you shoot a stage to make sure it is tight.
Enjoy!
Kyle
So you mean an extended choke tube just adds length to the barrel?
No, it is extended with a gnarled surface in order that you can remove/install it without a wrench. It only adds approximately 1" to the barrel's overall length.
Regards,
Kyle
I seeee....
Thank you
JMIS