If the only thing that changed was removing and replacing the stock then the answer should be torque or how it was torqued but since you shot it with different bullets from a different maker you may need to clean the barrel. Doesn't always happen but i have seen different bullets or powder for that matter mess with accuracy of a known load for a number of shots or until barrel is cleaned at least some. Those two places are where i would start with the first being the stock.
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