HK MR556 A4 Rifle

The MR556 is Heckler & Koch's commercial version of the HK416, a 5.56mm rifle known around the world. The A4 series is HK's latest update to the commercial HK416 and HK417 line. It adds fully ambidextrous controls, lighter weight, a slimmer profile and an adjustable gas regulator.

This is the 16.5-inch rifle, chambered in 5.56x45mm with a 1-in-7 twist. Like the HK416, it runs on a short-stroke gas piston. The piston system reduces carbon fouling and wear compared with direct impingement designs, which means less cleaning and longer life for the parts in the bolt carrier group.

The adjustable gas regulator lets you tune the rifle for suppressed or unsuppressed shooting. That's a real advantage if you plan to add a suppressor, since it helps control the extra back pressure and keeps the rifle running smoothly. The muzzle carries a flash hider on 1/2x28 threads.

The controls are fully ambidextrous, so left-handed shooters don't have to compromise. A 13-inch free-float M-LOK handguard has integral ambidextrous QD cups, and the HK416 six-position stock gives an overall length of 33.25 to 36.5 inches. The trigger breaks at 4.5 to 5.6 pounds, and the rifle weighs 7.67 pounds without a magazine.

HK includes one magazine, in 30, 20 or 10-round capacity depending on the model and where it's sold. If you want a 5.56mm rifle with genuine HK engineering and the piston system that made the HK416 famous, the MR556 A4 is the civilian way to get it.