Originally Posted by Social Casualty
I personally wouldn't fire the gun without the cap in place. The cap and butt plate need to be installed so the takedown detent, spring and takedown pin are held in place not to mention it unsafe to have the bcg rear open even though its held in place by contact of the upper/rear portion of the bcg to the lower, all it takes is one incident and your lights would be out.
In the photo the rear cap was not installed, its at the machine shop being anodized. If anyone is interested I am thinking of making some extra butt caps for the .22 AR pistol conversions. They will be low profile, very similar to the Sig P556 pistol butt caps but will be able to be installed and removed very easily unlike the P556's cap.
Very interested on the caps