“
The AR-57, also known as the AR Five Seven, is available as either an upper receiver for the AR-15/M16 rifle or a complete rifle, firing 5.7×28mm rounds from standard FN P90 magazines.
It was designed by AR57 LLC and[3] was produced by AR57 of Kent, Washington, United States.
The AR-57 PDW upper is a new design on AR-15/M16 rifles, blending the AR-15/M16 lower with a lightweight, monolithic upper receiver system chambered in FN 5.7×28mm. This model is also sold as a complete rifle, supplied with two 50-round P90 magazines.[1] The magazines mount horizontally on top of the front handguard, with brass ejecting through the magazine well. Hollow AR-15 magazines can be used to catch spent casings.
Unlike the standard AR-15 configuration which uses a gas-tube system , the AR-57 cycles via straight blowback.[6] A fully automatic version exists and was marketed as a competitor to the P90 and other personal defense weapons.[7]
Manufactured by the eponymous AR57 LLC, and chambered in 5.7x28mm, this upper is less powerful than the standard 5.56mm version, but it has certain tangible advantages, including reduced muzzle blast, a high practical rate of fire, nonexistent recoil, and the ability to use folding stocks. Since the buffer is located within the receiver, folding stocks may also be used for compact storage or carry.
To load, place the base plate of a standard FN P90 magazine into the recess on the front of the upper, then press the feed lip side down on the catch located above and slightly back of the bolt. To charge, pull on the right-side nonreciprocating handle and release. The right-side charging hand placement makes it accessible for operation by the strong hand. Since it only has to be operated once every 50 shots, the time penalty for moving the hand off the pistol grip isn’t too great.
Empties will eject downward through the nominal magazine well. Some people use a 20-round magazine body with the feed lips, spring and follower removed to act as a brass catcher.
The magazine has no provision for activating the bolt lock when empty, but the bolt can be locked open using the catch on the lower. The upper runs very cleanly and reliably, requiring no maintenance after the first 500 shots.
The AR57 comes with a medium fluted barrel, reasonable for a varmint rifle but excessive for a defensive carbine. Burning around six grains per shot, 5.7x28mm runs much cooler than 5.56mm, which burns four or more times as much. That yields much reduced muzzle blast and far greater heat endurance, of course at the cost of a roughly 40 percent slower bullet.
”
”