If the group sizes have change with the same everything else, I doubt the load is the problem. Things to look at:
1. Scope mount screws
2. Keep the crown for damage
3. Have you taken the stock off recently or change the changed the tension on the action screws?
4. Possible copper built up? Good barrel cleaning might help.
5. All barrels go south at some point, what is the round count?
6. Most important- you mentioned 0.25" groups. Where these shot under perfect conditions? If you hoping for 0.25" groups without the educated use of windflags on any normal day you going to be sadly disappointed. We all get luckly and post the occasional wallet group. Don't be concerned about a single group. The average of 5-5 shot groups tells you how well you gun actually shoots.

Luck, Tim