I can't think of any particulars that haven't already been mentioned. So just my general thoughts on it. If you are using the same, exact supplies as before, benching the rifles precisely the same way, aiming/shooting and using the trigger the same way then it absolutely has to be something to do with the gun itself or your shooting has changed.
Everything, sights, screws, stock warped or not warped and bore condition are possibilities. Screws should be snug, sights should be solidly in place and stock should not be warped enough for the pins to bind in the barrel underlugs. I've found that weighing and sorting ball is a waste of time for the hunter and casual shooter. I've fired super tight or one hole groups at 50 with random ball I've cast. I use tight loads that can still be seated with the wood ramrod. When my shooting sucks I know it's me with my bad eyes and old age. As Sherlock Holmes said, not verbatim, when all else has been has been proven wrong, the answer is that what remains however improbable it may seem must be the truth.