{"product_id":"mr556a4-upper-kit-5-56mm-11","title":"HK USA MR556A4 Upper Kit 5.56mm 11\" – Complete Piston-Driven Upper Assembly","description":"\u003cp\u003eThe HK USA MR556A4 Upper Kit delivers a complete 11-inch piston-driven upper receiver assembly chambered in 5.56mm NATO.\u003c\/p\u003e\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eType:\u003c\/strong\u003e Complete upper receiver assembly\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCaliber:\u003c\/strong\u003e 5.56mm NATO\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eBarrel Length:\u003c\/strong\u003e 11 inches\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eOperating System:\u003c\/strong\u003e Gas piston (HK416 system)\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eBarrel:\u003c\/strong\u003e Cold hammer-forged, chrome-lined, 1:7 twist\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCompatible With:\u003c\/strong\u003e MR556 lower receivers, AR-15 pattern lowers\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eIncludes:\u003c\/strong\u003e Upper receiver, bolt carrier group, charging handle, rail system\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eUse:\u003c\/strong\u003e SBR or pistol build (NFA compliance required)\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"Heckler and Koch (HK USA)","offers":[{"title":"Default Title","offer_id":47944170995967,"sku":"HK51000385","price":2220.95,"currency_code":"USD","in_stock":false}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0729\/0434\/3807\/files\/51000385d651.jpg?v=1766627634","url":"https:\/\/doublestackstore.com\/products\/mr556a4-upper-kit-5-56mm-11","provider":"Double Stack Store","version":"1.0","type":"link"}