I've got a plastic m16 knockoff with 4 RIS rails going around the barrel and a mossberg m590 which has one RIS rail on the top of it that's the same length as the bottom of the m16 rail, and I want a way to attach the two while still being able to get them apart if necessary. I would like to know what parts I would need and where I could get them, best answer gets 5 stars!
Spartan
Favorite Answer
buy 2 pairs of weaver rings, and take off the top half and place two bottom halves on top of each other and use the screws to hold them together so it has the rail grip on both sides. i say get 2 pairs cause just like mounting a scope, it's better to be holding on to two points and each mount like this uses one pair of rings.
Jack
There is nothing you can buy that will do this - the only way to stick the two together is to glue them. However, if you still want them to be able to be separated, I'd start by buying a riser mount.
http://cgi.ebay.com/UAG-OFFSET-1-2-WEAVER-PICATINNY-RAIL-RISER-MOUNT-E9-/390318995309?_trksid=p4340.m263&_trkparms=algo%3DSIC%26its%3DI%252BC%26itu%3DUCI%252BIA%252BUA%252BFICS%252BUFI%26otn%3D10%26pmod%3D290551250546%26ps%3D63%26clkid%3D433755766416394778
You can then glue this to the top of your shotgun, and then screw it onto your rifle. However this will make it hard to put any sights on your shotgun, unless you leave some of the rail on your shotgun uncovered.
Hope this helps