thanks everyone for the replies. I have heard horror stories of guns/parts/barrels taking a very long time to be returned from Mossberg after being serviced. And I'm up here in the Great White North so I can just imagine the BS I am going to have to go through to send gun parts back and forth...
Jmm, Whitey,
Will send pic tomorrow (posting this from work) ....in the meantime - no set screw, blade is dovetailed into welded-on base of sight. I believe it is Mossberg stock ghost sight system (wings on either side of rear sight).....definitely not XS system.
Thanks for your replies.
I received my 590a1 with ghost ring sights. Everything looks in order except - the blade sight on the front is backwards!! Tried tapping it out with a punch but she's snug. Any ideas or anyone experience same poor quality control in this respect?