Some powders are more sensitive to temperature extremes than others. Sounds like it's happened with a variety of powders, though.
I'm assuming you have a wood stock. You're keying on temperature variations, and what may be causing your problem is humidity, rather than temperature. If the stock is not sealed property, then the humidity fluctuations will cause changes in impact point - the wood swells and shrinks and changes the action/bedding relationship.
You didn't mention if your rifle was bedded. If not, then that's a great place to start. Then, inspect the barrel channel and action recesses to make sure there isn't any unsealed wood. If there is, get the stock warm and dry, and seal it with a good oil or polyurethane finish to keep the moisture out.
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