Photos above provided by way-out-west 2 of AR15.com forums.

Click Photos above for a larger image!

The FAB-10 is an AR-15 style rifle that was created in answer to the Violent Crime Control and Law Enforcement Act of 1994 (AKA Crime Bill) and subsequent additional laws in California that prohibited the manufacture of Semi-Automatic rifles with detachable magazines and other characteristics.

<please note, I am no expert on California Laws and if someone else would care to prepare a summary of the CA requirements, I will be glad to host your write up here!>

The FAB 10 system addresses these legal limitations through the use of an AR-15 style lower receiver that does not have a detachable magazine!  In the FAB-10, the magazine well is milled out from the top such that a 10-round magazine is fixed inside the lower via a rivet, but the magazine well was not opened through the bottom of the lower receiver.  The rivet that holds the 10 round magazine in place can be seen in the front section of the magazine well   (seen in the first photos above) as well as a #4 allen head set screw though the left side of the well into the mag (see pics).  

This lower receiver is loaded with a stripper clip via a special stripper clip guide.  The guide uses a round pin that is slid into a round hole in the lower receiver.  You can see the round hole in the photos above.  In the three photos that follow, you can see the special stripper clip guide then a photo of a loaded stripper clip mounted to the guide, and finally the way everything would look when loading the FAB-10.

Photos above provided by way-out-west 2 of AR15.com forums.

Click Photos above for a larger image!

The FAB-10 lower does not have any hold drilled for the magazine release or bolt catch.  Given that a user would need to open the lower receiver via the rear take-down pin when the internal magazine is empty, this is a good thing!