Olympic Arms OA-93

The OA-93 is an AR-15 derivative pistol manufactured by Olympic Arms. Lacking a buttstock or buffer tube, the OA-93 disperses recoil through a specially designed flat top upper receiver similar to the Armalite AR-18. However, the passage of the 1994 Crime Bill required Olympic Arms to perform modifications to the basic design to continue selling them: 
The first revision to the OA-93 was the OA-96 in which a 30-round ammunition well is pinned and welded in place so that it cannot be detached. In addition, the OA-96 has a button in the rear which opens the upper receiver and can then be loaded via stripper clips.
The second revision followed two years later. OA-98 used a detachable magazine but the body was skeletonized to reduce the weight below the 50 ounce restriction to allow the OA-98 to have one more feature to be compliant with the 1994 Crime Bill.
A piston driven carbine based on the pistol was made in 1993 and after the expiration of the Federal Assault Weapons Ban from 2004 to 2007.