The AO-40 is a bullpup assault rifle that was designed by Peter Tkachev.
Overview
The AO-40 was a rather oddball design with a very oddly-inserted box magazine chambered for a large number of 5.6mm (.22 caliber) bullets. However, this box magazine was also its biggest drawback. The box magazine used a rather interesting and potentially revolutionary system, which appeared to move three rounds through the box magazine through the force of the recoil.
References