I've found this to be a very accurate load in several 300's.
75g H4831 jumped .050"
Usually nets real close to 3,000 Fps. Kind of mirrors what Quickload is predicting above.
Did you run those cases over your expander ball before you checked them for concentricity? I've noticed the necks aren't perfect out of the box. Running them over the expander generally makes them show little to no run out.
With that said, I'd probably reload them for one go round personally...
I had the same thing happen on a rat shoot this spring. It was within the first hour of getting there and my 17 was down because of the squib and my stupidity for forgetting a cleaning rod. At least I had some other rifles to shoot so all was not lost.
Weird though, because that bullet was...