I know this is a bit late, but don't Mossberg 590a1's have a 10yr warranty? At least that's what I remember for mine. I'd call Mossberg to see if they can ship a replacement under warranty. I had the exact same thing happen to my 590a1. Luckily I watched it drop into the grass while I was shooting, so I was able to recover it, otherwise, I would have called Mossberg.
As I remember with my three 590a1's, they had super crappy small front "tiny" beads, I changed all mine out to brownells big bead, two silver and one gold, easy to do, drill a bigger hole, tap it, screw in the new bead , brownells sells a kit, makes a big difference



























