RE: Remington Supermag 870
Yes I have shot this choke before. It is one of the best out there. I would use 3 1/2 6' maybe x-tended ranges or regular winchester HV's. Pattern will be tight up to 20 yards , then it will open up gradually, no problem killing a bird at 50 yards. You should have around 40+bb's in the head and neck at 40yards and maybe 25-35 at 45 and then it drops off to around 20 at 50yrds. Also from what I've been told and seen make sure you wipe it down real good after it get wet, for some reason the ones I saw rusted up pretty quick. Get out and shoot it, you'll be very surprised on how well it shoots compared to factory chokes and other brands out there. Let us know how you do.