When I first got my Mossberg 930SPX, I mounted a forward sling mount- the type that mounts at the front end of the foregrip, around the mag tube and it is held in place by the mag extension.....had an issue (twice) where I think one of the rims of a shell got stuck in the mag tube. This removed the spring tension, allowing a couple of rounds to move freely in the tube, but of course, they would not feed. It also may have been the follower, but I'm not sure.

I'm thinking that, since there is a small amount of space made by the sling mount (appx1/8"), between the tube and the extension, it was enough to make a slight gap for the rim of the shell, or follower, to get stuck on.

Anyone have the same issue?

Example of the type of mount:
http://www.gggaz.com/mossberg-930-front-and-rear-sling-attachments.html

Yes.

What mag extension are you using?

Some brands (Nordic, maybe others) come as a 2 piece units so you can tighten the coupling first (holds the barrel and forearm tightly) then screw in the actual extension tube so the ext. tube still contacts the original mag tube (leaving no gap)

Factory Mossberg (made by Choate). Will probably look at one made by Nordic......

That will solve the problem.