When the AR-57 was manufactured, a 5.7×28mm (that is, the upper shell of P90) was directly assembled to the lower shell of an AR rifle, so the magazine was placed on it like P90, and the lower shell of the AR rifle was directly installed, so the magazine socket of the AR rifle was also equipped. .....
Since it is not manufactured in large quantities, it can be said that most of these guns are made of parts of other guns ... To tell the truth, I estimate that this gun was designed just for fun, because it was not sold to the military and police at all, and it was not equipped at all, just applied for a patent. .....