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|weaponinfo = The AR-57 is a carbine/personal defense weapon firing 5.7×28mm rounds from standard FN P90 magazines designed by AR57 LLC and is currently produced by AR57 LLC of Kent, Washington, USAin the United States. It is available as either an upper receiver package for the AR-15/M16 rifle or as a complete rifle . Versions are offered in both semi-auto only and in select fire, and full-auto for was marketed primarily to law enforcement agencies as a potential competitor to the FN P90.

While the AR-57 shares many outward similarities to the AR-15, there are a number of key differences. Unlike the a standard AR-15 configuration , which uses a gas-tube piston systemto work the action, the AR-57 instead cycles via straight conventional direct blowback in much the same way a submachine gun might. Where the differences become most apparent is with the ammunition. The AR-57 is chambered for the 5.7×28mm round developed by Belgian firearms manufacturer FN Herstal, and much feeds from standard FN P90 magazines. Also like the FN P90, the AR57 ejects spent brass downwards, it with casings falling out through what would normally be the magazine well on a standard AR-15. It is possible to use a hollow magazine inserted into this mag well as a brass catcher.