Well I have shot many guns. Many that people never even seen before. Here is what I think of the gun.
This gun would be very uncomfortable to hold. The Barrel is fine, He just need to improve the Butt-stock of the gun. The handle has to be able to fit into someone's hand. The Butt-stock should be slightly slanted and have grooves under the hammer so that the space between your thumb and Index rest comfortably. Also you need a way to extract the shell casing from the gun when it is fired. The Trigger Housing has to be rounded off so your trigger finger can rest inside. Also you got to draw out the Rear sights, so that the person can have better aim. The Laser is usually a box that is under the barrel (Check out Snakes Socom Gun in Metal Gear Solid). But unless you are going for a more futurist upgraded look I don't see a problem with the laser.
When gun is fired the top part of the gun detaches for a brief moment (err... slides backwards) to discard the used shell and the bolt hits home to have another round ready to fire. This happens in milliseconds.
http://www.youtube.com/watch?v=rth7YNtvb n8
This is the mechanics of a gun firing (took me a while to find this)!