My newest is a pistol from a PSA lower that includes a Fostech Gen II Echo trigger. Ridding that is two uppers. One in 5.56 and the other in 300 AAC Blackout. I have put a KX5 Flaming Pig on both and also Vortex Sparc on the 5.56 and a SIG Romeo 5 on the Blackout. The 5.56 has back up iron sights from Diamondhead and the Blackout has Magpul MBUS. With a complete sight system on each upper, I retain zero regardless of which I choose to shoot. As I had extra BCG's both uppers are complete with their own nickel boron BCG's and both have Radian ambidextrous charging handles.