Heckler & Koch USA has introduced the MR556 A4 upper receiver kits, making them available at HK dealers across the country. Enthusiasts can choose between 11” and 16” barrel lengths, both of which come with a lifetime barrel wear warranty akin to the complete MR A4 rifle. These comprehensive kits come with fully assembled components, including a bolt carrier group, a gas piston assembly, and an adjustable gas regulator, ensuring compatibility with most AR 15/Mil Spec lower receivers. The MR 556 stands out as the civilian version of the renowned HK416, featuring a short-stroke gas piston that improves reliability and requires less maintenance compared to the conventional direct gas impingement system of AR rifles. “We're excited to offer the A4 Upper Receiver Kits, which enable shooters to enhance their existing lower receivers without purchasing an entire new rifle,” Nathan Schueth, the HK USA Director of Sales & Business Development, commented. “For current MR owners, these kits provide a chance to upgrade their existing A1 with an adjustable gas block or to easily change the upper configuration.” Unveiled at the start of 2025, the MR556 A4 variant introduced numerous enhancements over the previous A1 model, including a lightweight barrel, a slimmer handguard, and fully ambidextrous controls, culminating in a weight reduction of about one pound.