Blackmaxx .575 was (I assume still is) made by Carlson. Mine is ported as David K. stated. I also special ordered an Indian Creek .570 ported back when I was doing my testing, but for my style of hunting (mostly hardwoods, shots typically under 40 yards), the BM .575 provided a more evenly distributed uniform pattern at one third the cost of special ordered IC .570, IN MY GUN, and it was forgiving enough up close for those 10-15 yard shots when he slips in on you silent. I handload/shoot 3" 1 5/8 ounce TSS #9s.Layne,
Yes, Andy said he tried several chokes in his 870 and ended up with the Cabela's BlackMax in .575" so that's what I bought...
Blackmaxx .575 Turkey Choke (REM 870 20G)