The HK MR556 A4 SBR is Heckler & Koch’s AR-pattern semi-automatic rifle in 5.56 NATO, built with an 11-inch barrel (HK part no. 81001048). The short barrel and shoulder stock make it a short-barreled rifle, which keeps the overall package compact for vehicles, home defense and close-quarters training. It feeds from 30-round magazines, the standard capacity for the platform. The MR556 A4 line is HK’s civilian take on the rifles it builds for military and police buyers, and this configuration is the short one. It suits a shooter who wants HK build quality in the handiest possible length.

Key Specifications

• The chambering is 5.56 NATO, the standard AR-pattern cartridge with the widest choice of factory loads.
• Barrel length is 11 inches, short enough to keep the rifle quick to handle in tight spaces.
• Magazine capacity is 30 rounds, the standard AR-pattern count.
• The action is semi-automatic, one shot per trigger pull.
• The configuration is a short-barreled rifle, a shoulder-stocked rifle with a barrel under 16 inches.

Frequently Asked Questions

How long is the barrel? The barrel is 11 inches, which is under the 16-inch line and is what makes this MR556 A4 a short-barreled rifle.

Do I need ATF approval to buy this? No. As of October 9, 2026, ATF no longer requires Form 4 approval, registration or a tax stamp for short-barreled rifles. It transfers on a Form 4473 with a background check through a Class 3 (SOT) dealer. State and local laws still apply. Taking an SBR across state lines still requires an approved ATF Form 5320.20.

What magazine capacity does it use? It is a 30-round rifle, using the standard AR-pattern capacity.

Buy the HK MR556 A4 SBR, 5.56 NATO, 11-Inch

An 11-inch MR556 A4 is about as compact as an HK rifle gets while still wearing a stock. As of October 9, 2026, this short-barreled rifle transfers on a Form 4473 with a background check at your Class 3 (SOT) dealer, with no Form 4 or tax stamp; state and local laws still apply. Order through Heckler & Koch‘s short-barreled rifles lineup and our Lubbock, Texas team will handle the transfer as soon as it is available to ship.