You can mount a picatinny rail on a Mossberg or Remington pump. Get a laser --TNVC sells class 1, Newcon Optik sells class 3 lasers. Based on the price, I'd think they'd be good --they do make other military contract stuff, just not the lasers. Not much on them though, and the older ones (which look different now) supposedly had problems. This was years ago, don't know about now, and a bad rep. can follow you for a while. But for shotgun distance, I suppose class 1 is all you need. The LDI DBAL's are filled with epoxy I hear. I'd ask about recoil though, still.
Then whatever laser I got, I'd get one with a QD lever so it could be removed from the top rail on the receiver. Since this is going to be your only aiming device and you want it to be accurate, this is where you'll want to mount it. Sounds odd, I know, but we used to have to mount PEQ-2A's to the feed tray cover on SAW's for night missions before they finally got rails on the handguards. This totally obliterates any other sights. That way you can take it on and off easy and replace it with an EOTech on a QD if you like (which is awesome for a shotgun) or if the rail doesn't get in the way, irons. With helmet mounted PVS-14 and laser on the shotgun zeroed (or patterned) to your liking, you'll be able to shoot this from the hip easier than the shoulder, most likely. I liked to hold laser aimed weapons under my armpit, holding the stock in tight with my arm.
Meprolight makes a reflex sight, 30mm, similar to the Trijicon ACOG RX01 but bigger. It has a visible laser built in on one side and an IR on the other. The IR laser is about 5mW, so it is a low end class 3 laser. You can also buy this one it seems, as I guess it is imported and doesn't have a military designation either. I forgot the site I saw it for sale on. This would be a one stop fix: reflex sight and laser all in one, day and night. As far as I know, this and the Newcon Optik are the only class 3 ones you can buy without FDA crap.
You can still find the EOLAD if you look (IR laser built into an EOTech sight) and wasn't that sight on the Tavor an inexpensive, low class 3 IR laser/reflex combo? If so, that might be a good cheap way to go for a shotgun. There used to be a bunch of those for sale on Ebay a while back.
You actually have lots of choices, provided they can all stand up to the recoil. Mounting on receiver is the best with all of them. And at shotgun ranges for what you intend to do, class 1 lasers aren't really a problem unless they get washed out by your illuminator(s). If you want class 1 lasers, give the guys at TNVC a call and ask them, they can surely fix you up and help you get what you need without going overboard if wish. Really good guys, who I do my business with.
