Given the use for the 15 22, I elected to install the Walther PS 22 purchased from Midway. I currently have a m&P15T with an Aimpoint ML3 installed and like that system very much. When I purchased the 15 22, I chose the Walther PS22 because it is similar to the ML3 but much less expensive. It comes with a very sturdy mount and it coindexes with the factory iron sights. I also purchased a pair of Magpul BUIS sights to replace the factory sights. The factory rear sight will be installed on an early MP15 that is the standared m4 configuration. I purchased an Aimpoint Swede military sight from Midway when they had them. That is how I configured that early M4. They are great rifles. When I get a chance, I will post a photo of them.