Look at the design and size of the follower to help determine if it will help or hinder capacity. The follower that I chose for my 590 7shot(6+1) model:550778 to use is very similar to the factory one accept for the mere fact that it is aluminum, anodized orange, and a hole in the center to decrease any pressurization as it moves in the magazine tube. It is very much like a cup design with the mag spring behind it, so most minimal in size. I used that follower with the factory spring and factory tube extension on my mag tube and capacity wasn't increased. I then switched to the Wolff spring and it made just enough space to clear an extra round with the mag spring completely "100%" compressed making it into a just barely 7+1. Adding a slightly larger mag extension that now sits flush to my muzzle now didn't give me any more capacity for another round but the now less spring compression was more reliably acceptable. Not sure if my experience will be the same as yours but I figured I would just share how things worked out for me.