With 270 velocities and being that close I think you just experienced a blow up that can happen with normal shelf ammo when you're up real close and stricke some bone. The core-loct isn't the hardiest of loads but usually does fine with normal conditions. You were a trifle close but I'd be disappointed in that performance. I'd run it by Remington.

You are correct to consider that the Partition would have probably performed better, but who knows, it may have just gone one through with little expansion........