This is a great combination - Holosun HS510C 3x Circle Dot Sight w/HM3X Magnifier Combo

I'm buying this for the third time. One of the great things about the magnifier is that it comes off real easy so if you don't want to have it on there you can take it off and then throw it back on without having to re zero or anything. You can put this magnifier up behind any other optic as well. I use it for my 503g acss.

I also recommend you get a large ambidextrous charging handle because it's hard to reach the standard size charging handle.

There will be a slight point of aim point of impact shift when you use the magnifier. Approximately 3 in at 50 yards. 0 with the magnifier because it will not make that much of a difference when you're not using the magnifier.