Xtreme Chokes of California developed the prototypes for the Krieghoff titanium chokes, which are now standard equipment on K-80 shotguns.

Now working on their own, they have refined their original design into an Xtreme extended choke which is available for the Krieghoff K-80 factory-threaded barrel. They are also offeriing the Xtreme extended choke for the Beretta Optima-bore barre and the Perazzi factory-threaded barrell.
$105 each (Cyl, Sk, IC, LM, M, IM, F constrictions)

Also available for immediate shipment are Xtreme extended titanium chokes for the Krieghoff K-20 barrels, in all gauges; 20, 28, 410.
$135 each (Sk, IC, LM, M constrictions)

Their newest innovation is the Xtreme collared choke (pictured below) for the Krieghoff K-80 12-ga barrel. This choke design features a 360-degree ported choke tube and a rotatable collar which covers the ports, channeling the gases through the two ports on the collar itself. This design helps control muzzle rise on recoil and is intended to eliminate the need to ruin the value of a barrel by having it ported instead.

This patented product is available and ready for shipment.
$165 each (all constrictions from Cyl to Full)