Got my Undertaker choke for my Tristar Viper today. Hope to shoot it soon if the ice will go away. I will try and post pics.
I've had two, a ported .675 and an unported .660, the .660 worked best for me in a Win. 1300.
I have one for my 1300 too. It's the non ported .675. I would average 170s with hevi 3/2/6. Best was 196.
The one I have is the ported one. And it says it is .665 constriction. I will try and shoot tomorrow and post pics.