Depends on how much brass you have for the rifle. When I got into 6.5 CM business I ladder tested, and group shot on virgin brass, because I started with 500 pieces. Once they were all shot once I stuck with the same load, never retested, and didn't notice a change.
But if you have 100 pieces of brass for a rifle, it's not too far down the road that you've shot them all once. After a .002" bump there's be nothing wrong with testing groups within the node again, but I wouldnt re-ladder test.
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