{"product_id":"hk-mr556-upper-receiver-kit-for-ar15-m16-m4-piston-system-5-56mm-51000385","title":"HK MR556 Upper Receiver Kit for AR15\/M16\/M4, Piston System 5.56mm, 51000385","description":"\u003ch2\u003eProduct Description\u003c\/h2\u003e\n\u003cp\u003eThe HK MR556 Upper Receiver Kit is a complete upper receiver\/barrel assembly designed to retrofit Mil-Spec 5.56mm AR-style rifles (AR15\/M16\/M4 pattern) to HKs piston and pusher rod operating system. By replacing the traditional direct-impingement gas tube with a closed piston system, this design helps keep hot carbon fouling and waste gases out of the receiver area for cleaner operation and improved reliability. This HK piston-driven concept is the same key feature that contributed to the success of the HK416 platform used by military and law enforcement customers. The upper ships in an HK soft case for storage and transport.\u003c\/p\u003e\n\n\u003ch2\u003eProduct Highlights\u003c\/h2\u003e\n\u003cul\u003e\n  \u003cli\u003eComplete HK MR556 upper receiver\/barrel assembly to retrofit Mil-Spec 5.56mm AR-style rifles\u003c\/li\u003e\n  \u003cli\u003eClosed piston and pusher rod system reduces carbon and gas blowback into the receiver vs. direct impingement\u003c\/li\u003e\n  \u003cli\u003eDesigned for AR15\/M16\/M4 pattern compatibility (Mil-Spec 5.56mm)\u003c\/li\u003e\n  \u003cli\u003eKit shown with bolt carrier group, buffer, and action spring components (see product image)\u003c\/li\u003e\n  \u003cli\u003eShips in an HK soft case for protected storage and transport\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch2\u003eSpecs\u003c\/h2\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003eBrand:\u003c\/strong\u003e HK\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eProduct Type:\u003c\/strong\u003e Upper Receiver Kit (Upper receiver\/barrel assembly)\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003ePlatform Fit:\u003c\/strong\u003e AR15 \/ M16 \/ M4 (Mil-Spec AR-style rifles)\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eCaliber:\u003c\/strong\u003e 5.56mm\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eOperating System:\u003c\/strong\u003e Piston and pusher rod (closed system; replaces standard gas tube)\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eIncluded\/Shown Components:\u003c\/strong\u003e Upper receiver\/barrel assembly; kit shown with bolt carrier group, buffer, and action spring (see image)\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eCase:\u003c\/strong\u003e HK soft case (included)\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eManufacturer Part Number:\u003c\/strong\u003e 51000385\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eUPC:\u003c\/strong\u003e 642230270220\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003e\u003cem\u003eDisclaimer: We strive to provide accurate and up-to-date product descriptions, specifications, and images; however, errors or omissions may occasionally occur. We are not responsible for any inaccuracies or discrepancies in the content provided. If you notice anything incorrect or unclear, please contact us so we can correct it. When in doubt, we recommend verifying details directly with the products manufacturer.\u003c\/em\u003e\u003c\/p\u003e","brand":"HK","offers":[{"title":"Default Title","offer_id":44077253197946,"sku":"FLX-178701","price":2161.98,"currency_code":"USD","in_stock":false}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/1679\/0365\/files\/283964809.png?v=1767656055","url":"https:\/\/tlooutdoors.com\/products\/hk-mr556-upper-receiver-kit-for-ar15-m16-m4-piston-system-5-56mm-51000385","provider":"TLO Outdoors","version":"1.0","type":"link"}