Went shooting today to test some extraction issues with my AR10 I shot this group. a lot of my groups look like this vertically stringing. The shooting range right by my house has concrete T shaped benches that make it really hard for me to get directly behind the rifle. They do not allow prone shooting on the main range so I am stuck with seated position. any ideas on what I am doing wrong ,cheek pressure trigger pull. I shoot off of a front sand bag and a rear squeeze bag Thanks