With an ithaca 37 - If you hold the trigger down, and pump - it will fire as quick as you pump - its supposed to - you do not need to press the release - I don't know about a mossberg though - but would guess its the same.

I had a gun that would "misfire" every now and then (old savage arms) - but never when I practiced - What I found out was that when I "quietly" loaded the gun in the morning - I apparently wasn't properly working th action to reset the firing pin - Thus the misfire (and very quick pump - and shot) - In a couple cases I never go the shot off after pumping it again, in a couple others - I did.

I got rid of that gun.