Good advice. Usually it's the large steel shot that causes problems in the fixed full chokes.seegree...
Check with your booklet. Or if the choke states "steel only" or "lead only".... or something along those lines.
Also if you shoot an email to Winchester i am sure they would answer your question.
But one thing to do is go PATTERN your gun. Because your full choke might throw the shot low and left. Where you mod, IC will have a more consistent pattern. Draw a 30 in circle, aim in the center, and shoot. See where the bulk of your pattern is... with any choke u want to use. Then do again at other distances.
Then what I have done (might be going over board).... I will find out how many pellets are in each shell....(you can find this info on the internet.... 1 oz of #2 in 20 ga. is XXXX of pellets)..... then I will count how many I have in that 30 in circle. I like to have 60-65% of the pellets in that circle with more the better.
Yes when I tested out my beretta extrema 2 with different full chokes, shells, and pellet sizes..... my friends thought I was nuts. I will have to say it has worked out good for me because now I know what shoots good out of my gun and at what ranges.