The Black Rain Ordnance Milled Upper Receiver is precision-manufactured from billet aluminum with a durable black anodized finish for .223 Remington caliber builds.Black Rain Ordnance Milled Upper Receiver.223 Remington caliber compatibilityBillet aluminum construction for superior strengthBlack anodized finish for corrosion resistancePrecision machined by skilled American craftsmenModern sporting rifle platform designBuilt to Black Rain Ordnance's exacting standards using only American materials this upper receiver delivers the precision and quality that serious firearms enthusiasts demand for their custom builds.