The Alexander Arms UST-17ST is a .17 HMR AR-15 upper receiver assembly that comes as a standard with an 18\" button-rifled, 1:10 twist barrel. The barrel boasts straight flutes and a muzzle threaded 1/2-28 TPI RH suitable for standard .223/5.56 muzzle devices. The standard handguard provided is the Alexander Arm\'s mid-length, G10 fiberglass composite non-vented mid-length free-floating handguard.This package includes the necessary lower receiver conversion parts kit and two 10-round magazines. Designed with a blowback operating system, the weapon exhibits exceptional performance. The upper has a weight of 4.5 pounds, making it both robust and manageable.This assembly is fully completed, with easy compatibility to any standard-specification lower receiver simply by installing the included parts kit.