every shell make has a differnt burn rate for powder so some may max out on burn at a certain length. trust me the heavier loads have a slower burning powder to keep it to saami spec. rule of thumb, is that you loose around 10 fps per inch shorter that 26, and you will loose center core pattern , this is why your pattern is so open. if you dont believe me there is mo mistake all the still shoot turkey target / and card shooters shoot 30+ barrels . now you can get it to shoot awsome , but it will take some work.