Heckler & Koch HK51000384 MR556A4 5.56 Upper Receiver Kit (16.5″)

Description

Product Overview

Heckler & Koch MR556A4 Upper Kit (HK51000384) is listed under Accessories / Upper Receivers. Source facts verify 5.56mm upper kit designation, inclusion of bolt and buffer, an M-LOK handguard, and Package Qty: 5.

Why This Product

Verified inclusion of bolt and buffer and an M-LOK handguard are important for buyers assembling or replacing upper receiver groups and planning parts compatibility. Package quantity (5) matters for bulk procurement.

Key Verified Specifications

• Brand / Manufacturer: Heckler and Koch (HK USA) (product-275578:f002, product-275578:f006, product-275578:f007)
• Model / SKU: HK51000384 (product-275578:f013)
• Product categories: Accessories; Upper Receivers (product-275578:f003, product-275578:f004, product-275578:f005)
• Package quantity: 5 (product-275578:f008, product-275578:f011)
• Verified inclusions: Includes bolt and buffer; M-LOK handguard (product-275578:f009, product-275578:f010)
• Availability status: in stock (product-275578:f014)

Appropriate Use Cases

• Ordering upper receiver kits for gunsmithing, assembly, or replacement where an included bolt and buffer reduce the need to source those specific parts separately (product-275578:f009).
• Buying in bulk (Package Qty: 5) for stock in a parts department or retail lot (product-275578:f008).

What Customers Should Know

• Source facts indicate a 5.56mm upper kit but do not provide complete compatibility details with lower receivers, specific barrel twist rate, gas system length, or included sights—verify exact fitment and technical specs with the supplier before ordering (product-275578:f009, product-275578:f010).
• Confirm whether the included bolt and buffer are complete and ready-to-install assemblies or partial components; the source facts only state their inclusion (product-275578:f009).
• Package Qty is 5—check packing configuration and shipping requirements when placing an order (product-275578:f008).