I own 2 Mossberg 835's and had the exact same issue with 1 of them. 2 guns with the same chokes and same shells shot 2 totally different patterns from the same distances. Only way I was able to fix it was with a red dot sscope. I hate to say it but its probably going to be your only fix as well or at least a set of open sights with an adjustable rear sight. Good luck and dont be discouraged because at least you have some options. Good luck.