It's also the same 30mm BSA RDS that used to come in the factory carbine package, and that HP used to sell on their .net accessories page. I got one when I bought my alphabet soup 4095 8 years ago.I used this BSA red dot scope. I believe it is 30mm. I bought it off Amazon and it was very reasonably priced. It has perfect co witness with no riser. It's very easy to use the iron sites when the red dot is not turned on. I did have to cut about a 1/2 inch off of the front of rear site to get it to fit but that was easy. I removed the rear site and used a dremel tool, only took a few minutes.