Thought some of you would find this interesting, don't see too many of these in the civilian world.
The upper, it uses a modified Colt upper reciever by the looks of the markings.
A look through the upper.
The ejector.
The bolt, which uses the M16 extractor and firing pin. The firing pin has a spring in front of it though. Which you can see in the next pic.
The other side.
The bolt face.
The fake portion of the barrel. The actual barrel is only about 12" long and is rifled.
The only pic I had of the mags or ammo. I should have taken some more of those. The mag has a coiled piece of metal it uses to push up the follower which is interesting. The sim round is a short 9mm case with a plastic bullet filled with colored detergent. The travel at about 450fps, which makes them a bit more painful than a paintball. They'll usually break your skin if they hit on just clothing.