Leave it alone for now. The one Howa Vanguard I worked with shot better once in a wooden stock, action bedded and barrel floated. I would be suspect of the middle pressure point. The loose front screw might indicate the rifle wants to be free floated. I would test with shims and see if it improves, if so eliminate the middle hump. If it improves then I might try the shim again and do a full free float. Also coat the trigger group with prussian blue and check for contact points. But it could have been the change in bullets and or a fouled bore all along. I doubt that you would go wrong in glass bedding the action and free floating the barrel once you have eliminated the trigger the contact question. If it does not improve then easy enough to add a front V block pressure point again. But the real issue is changing more than one variable at a time.

"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli