It's usually from the barrel not locking up and going to the same position when manually loaded, compared to it cycling from fire. If you pull it back and let it run home on it's own and it still does it. Usually a tight bushing to barrel fit is the only way to get it to have consistency from first shot to the rest. I have known some fellows to cheat though. They load 7 for the first 5 shot. The first is popped at another target. 5 are grouped, the last is reserved for the first shot on the next group with a fresh mag behind it.