Panzer Arms AR57 ULT Complete AR-15 Upper Receiver - 5.7x28mm - 12"

The Panzer Arms AR57 ULT Complete AR-15 Upper Receiver converts any mil-spec AR-15 lower to fire 5.7x28mm ammunition, pairing a 12" lightweight barrel with a top-loading design that ejects spent cases down through the lower's magazine well.

Features:

• 12" lightweight steel barrel chambered in 5.7x28mm
• Top-loading design, downward ejection through the AR-15 magazine well
• Alloy monobloc receiver integrating barrel, muzzle brake, BCG, buffer, and screws
• 8620 alloy bolt
• M-LOK handguard, melonite black coating
• Ambidextrous magazine release
• Reversible charging handle
• 50-round magazine included

Converting an AR-15 lower to 5.7x28mm this way skips the need for a dedicated 5.7 firearm or a separate lower receiver, and the monobloc receiver design keeps the barrel, muzzle brake, bolt carrier group, buffer, and screws integrated into one durable unit rather than a collection of separate parts. The 8620 alloy bolt is the only moving element in the system, simplifying maintenance.

Because this 12" barrel measures under 16", this complete upper is intended only for an AR pistol or a legally registered short-barreled rifle — attaching it to a standard rifle lower without the correct configuration violates federal law.

Panzer Arms has designed and manufactured rifles and shotguns for 48 years, beginning with hunting rifles in Turkey in the 1960s and now bringing modern firearms designs to the market.