new Mossberg 500 pump but every time i shot the shell it got stuck,couldnt eject it.Had to take the barrel off to get the shell out every time.I shot the Winchester Xtended and another shell and didnt have that problem.
Sounds like the brass at the bottom is swelling up'
And getting stuck.
Try rubbing some lube of some kind on the brass.
And try it again.
I had this happen with a 22 with federal bird shot.
It would swell up a little after being shot.
I would rub some oil on the bottom of the case
Before loading them and they,
Would eject like normal.
Hope this helps