this may not be it but the first thing I would check is if the choke tubes are in all the way. Even a little loose can through off the patters. After that I would try different ammo.
sorry I know im not alot of help here.
"I ask, Sir, What is the militia?" "Its the whole of the people. To disarm the people is the best and most effectual way to enslave them" -George Mason Co-Author of the second amendment.