.30 Impact Slugs

Okay guys, those of you with .30 impacts, what are your slug recipes? Right now, my Impact is liking the VK 50 grainers at exactly 928-930 through Slug liner A. Anything above or below that speed is a flier. Looking for more forgiveness. I’ve heard some guys having success with Nielsen’s or even good luck with pellet liners. So what’s everyone else getting best results with?
 
Have the NSA 43.8 shooting at 952 
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50yds