I have a 12 ga tracker and it'll put two Winchester 2000 fps sabots right next to each other, and the third shot opens up a bit. I looked down the bore on that 3rd shot and there was smoky plastic, big streaks, and residue in the barrel. I think the 2000 fps slugs foul the barrel a lot more. This might also explain the poor groups you got with the Remingtons, since you shot the Remingtons after the Winchesters on the 50 yard target, the plastic fouling might have messed everything up.