Hey all I have a Burris fast fire II. I would like to mount on my
15 22. My question is, what height riser would I need to use to get it to Co - witness with the Magpul flip up sights? Don't want to order the wrong one. Thanks

I needed a 3/4" riser, but that was for a different sight.
Mount your Fast Fire on the rail, measure up from the top of the rail to mid-point of the glass on the dot. Subtract this number from the same measurement to the center of the aperture rear sight. This will get you real close. That is how I did it and my sights co-witness perfectly.

It helps that the iron sights are sighted in to begin with though.

Thanks. I should have thought of that. Must have my brain on hold.

I use a Burris ARF-3 with a fastfire II on my pistol and the ARF-3 with a fastfire III on my rifle and they work perfect.

J