From what I understand, the Dead Coyote choke was cut to two different diameters, one at .660" and the other .680". If you had received the .660", I HEARD that Carlson's would exchange it for a 0.680" for free if you mailed it to them.
I personally use a 0.680" Carlson's Dead Coyote choke with the Bismuth T shot from Carlson's, the Dead Coyote shot. I've also used it with #4's. Fantastic patterns, and great knock down power. Really extends the range of my shotty.
