ORIGINAL: rem 700
I'm gonna go out on a limb and say this isn't always true. I think the Powerbelt, being bore sized instead of .452 at nearly the same weight, has a smaller bering surface and SD so it may be getting over-stabilized and wobbles after a certain distance. This may be why 295-400gr Powerbelts and concialsare more popular than lighter weights in sabots. Just a thought..
If it's stabilized at 100 yds it probably is at 200 as well. He didn't say that it was keyholing so I doubt stability is an issue. But the larger diameter probably means it has a lower BC than the 250 Shockwave. I've noticed that bullets with a higher BC group tighter at 200 yards even if they shoot similarly at 100. The only thing that I can figure is that BC isthe factor there. In other words all else being equal a higher BC bullet will group tighter at longer ranges.
I'm not talking different weights though so there could be something I'm missing here.