Just curious if anyone has mounted a RDS on a quad rail in a scout type of setup on a fixed carry handle AR, and how well it works. Working on getting a Colt 6450, and kicking around ideas for optics, but not too crazy about putting one on top of the carry handle. The specific rail in question would be a KAC RAS.
It CAN be done and has been done, but the preferred method in this case would be to add an a.r.m.s. carry handle gooseneck… about the only a.r.m.s. product I know of that has not recieved a ton of hate. I see no ill effect of putting a rds on a solid reputable ff rail. Some claim a possible change in poa/poi. While this is possible, I think the risk can be lessened by mounting the optic as far back on the rail as possible. I don’t see a rail of solid manufacture being any less stable then a gooseneck being attached to a carry handle by a thumb screw. None of this, however should be used as advice, as I have experimented with neither. 
Wow, talk about lose/lose.
I have used the goosenecks for A2s, but I have no idea if it is compatible with a railed HG.
Definately wouldn’t want to mount it on top of the A2 “carry handle”.
Really, for the cost of the mount and added failure points I would probably pick up a railed upper and do a barrel/HG swap.
This, of course, would be your best bet. Hock your upper and snag a flat top.
Yes, I see this a viable option. And I know this isn’t really the correct forum for this, but it is important to use a 9mm upper, or would it be acceptable to use any upper?