Most 5.7×28 arms are short-range defensive designs. Planned bolt actions from Savage and others did not materialize, so this essentially small game/varmint load had no platform from which to realize its full potential. I originally scoffed at the AR57 upper as being much larger than a PS90, but have changed my mind now that I am more interested in accuracy.
5.7×28 is a 150 yards round, so I think that a 3x scope would suffice for most needs. When Primary Arms brings out the 5x prismatic later this year, I’ll swap. Conventional scopes are just too long for the magazine to clear them on loading, though with case the magazine could be inserted under the objective bell from the side. I have not yet shot this combination, looking forward to find out how it works.
The original purpose of this was to amuse left-handed kids (thanks to bottom ejection), but it might actually have a practical use beyond range plinking. Since the rear sight spot is occupied by the scope, I added a tiny Crimson Trace laser to the top of the forend as a backup sighting option.