This complete upper receiver is ready to drop onto your AR-15 lower receiver and convert it into a 5.7x28mm firearm making it an AR-57!This 5.7 upper ships with a 50-round P90 style magazine included that attaches above the barrel allowing the original lower receiver's magazine well to be used as an ejection port.Also included is a 5.7x28mm optimized buffer that suits the lighter recoiling round. The upper's handguard uses MLOK slots along with small 1913 Picatinny rail sections to allow for a variety of customizations and configurations by the end user.Milled from a block of aluminum alloy this upper is a lightweight and rugged receiver. 5.7x28mm Complete Upper 16" - AR57Includes one 50-round magazineIncludes 5.7 Optimized BufferDrop-in ready Complete UpperSimply add your favorite aiming solution to this upper receiver drop it onto your lower fill the included magazine up and slip the included buffer into place and you're ready for range time!The 5.7x28 cartridge is a light-recoiling and capable round that is perfect for your AR. With many manufacturers getting into making 5.7 products now is the time to pick up an upper receiver chambered in this advanced NATO cartridge!Order your 5.7x28mm complete upper receiver online here!Save time and money when you purchase 5.7x28mm ammo at Ammunition Depot! Our online inventory of cheap ammo for sale is available from the top brands you know and trust.In the market for a new rifle magazine? For big savings and fast shipping shop our online inventory of low-priced Rifle Mags for sale.Caution : Must install buffer before use