Thread: Point of impact shifts between serials?

Down at the range today doing some sighting in.

6 targets. 5 shot group on each target.

First 3 targets the verticle main of impact didn't change.

However, targets 4 and 5 had a significant change in main point of impact in terms of verticle. It was about 3 inches low. All the groups were still tight.

And then target 6 was the same as the first 3 targets.

The air temperature would have come up no more than 2 degrees during the course of the firings. The gun was cooled before moving between targets. Shooting techniques remained the same. Same ammunition batch.

What could this be??