Have any luck with any chokes with heavyshot 13
I haven't seen anyone on here yet experimenting with the Optima HP. I would see what William at Sumtoy has for it. He might save you some legwork. Pure Gold is also manufacturing an Optima HP turkey choke in .660 & .670. My experience with Optima + would steer me toward the .670.
We have doe testing with the A-400 Xplor with our own Nitro Company loads. Using a Rhino .670 choke tube and our Item H517C (2-7/16oz) 4x5x7 hevi-shot, you can get between 300 to 330 pellets in a 10" circle at 40 yards. Our M517C (2-7/16oz) 4x5x6x7 mega-weight will get between 280 to 330 pellets in a 10" cirlce at 40 yards as well. The gun shoots very well. Indian Creek is making a choke for it as well and should be ready in about a week or so.
I have one and some hevi 6s and a pure gold 660 just haven't made it out yet