Heckler & Koch displays HK421 7.62 mm light machine gun in Germany for rapid assault units.

Germany’s Heckler & Koch has presented the HK421, a lightweight 7.62x51mm NATO belt-fed machine gun designed primarily for dismounted infantry operations.

At Enforce Tac 2026, Germany’s Heckler & Koch displayed the HK421, a lightweight 7.62x51mm NATO belt-fed machine gun which was first unveiled in 2023. The HK421, developed to be lighter than the MG5 while maintaining sustained fire capability, is designed primarily for rapid, dismounted infantry operations. Positioned between traditional universal machine guns and newer lightweight belt-fed systems, the HK421 retains MG5 design elements while introducing shorter barrel options, modular mounting interfaces, and compatibility with NATO ammunition and accessories.
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Weighing between 8.3 and 8.7 kg, the HK421 is a gas-operated, open-bolt machine gun chambered in 7.62 NATO, positioned between traditional general-purpose machine guns such as the M240 and newer lightweight belt-fed MGs such as the SIG XM250. (Picture source: Army Recognition)

The HK421 is a 7.62 mm x 51 NATO belt-fed machine gun derived from the MG5 and developed by Heckler & Koch under Projekt HK421, initiated in 2017 to create a lighter, modular weapon for an assault rifle-like usage profile in dismounted, non-tripod employment. The HK421 targets infantry and special forces requirements, bridging the space between universal machine guns such as the MG5 and FN MAG and newer lightweight belt-fed designs like the FN Evolys 762 and SIG XM250 in 6.8 x 51. The concept centers on a weight class of eight to nine kilograms, combining reduced mass with sustained-fire capability and a quick-change barrel for prolonged engagements. It retains common handling logic with the MG4 and MG5 families to ease transition for operators already trained on universal machine guns. The HK421 can also be mounted on reconnaissance vehicles, field mounts, and FN weapon stations while remaining optimized for hand-held use.

The HK421 operates as a gas-driven weapon with a long-stroke gas piston and a locked rotating bolt head, firing from the open bolt and supporting both burst and sustained fire. Feeding is from the left using DM60 or M13 NATO disintegrating link belts, with cartridge cases and links ejected to the right to improve balance when using ammunition boxes under the receiver. A hydraulic buffer within the bolt group stabilizes cyclic function and mitigates recoil impulse. The safety mechanism allows selection in any loading state, with ambidextrous levers and the ability to cock the weapon while set to “Safe,” reducing the risk of unintended discharge if the bolt is released before full rearward lock or if the pistol grip module is removed. The system withstands barrel obstructions in accordance with NATO AC225 / D14 requirements for soft and steel core ammunition types DM11 A2 and DM151.

Two principal barrel configurations are available, 330 mm, equivalent to 13 in, and 421 mm, equivalent to 16.5 in, both equipped with a quick-change mechanism and carrying handle. With the 330 mm barrel, muzzle velocity reaches 730 m/s and muzzle energy 2540 J, while the 421 mm barrel delivers 780 m/s and 2,900 J. The barrel profile incorporates four grooves with right-hand twist in a groove-and-land configuration. The effective main combat range is 600 m, while the accurate suppressive fire extends to 1,000 m. A 3-stage gas adjustment supports normal operation, sustained fire, and suppressed fire modes, enabling control over the rate of fire under varying conditions. The weapon is compatible with suppressors and supports day and night combat configurations.

In its lightest configuration with the 13 in barrel and para-buttstock, overall weapon weight is 8.3 kg, increasing to 8.5 kg when fitted with the HK416 A8 buttstock. The 16.5 in barrel configuration weighs 8.5 kg with para-buttstock and 8.7 kg with the HK416 A8 buttstock. Barrel weight is 1.7 kg for the 330 mm version and 1.9 kg for the 421 mm version. For the 13 in configuration, overall length ranges from 810 mm with buttstock retracted to 995 mm extended, with a width of 125 mm, a height of 240 mm, and a sight radius of 290 mm. The 16.5 in configuration measures from 895 mm to 1,085 mm under the same conditions, with identical width, height, and sight radius. Buttstock adjustment travel is 185 mm, with the first detent at 114 mm and subsequent detents every 14 mm, totaling five positions.

The receiver uses stamped sheet metal construction in a compact layout and integrates an interface compatible with FN MAG and Minimi Mk48 tripod mounts. Beneath the receiver, a mounting point accommodates ammunition containers or bags, adaptable for FN ammunition boxes, including 60-round and 120-round configurations. The top cover incorporates a STANAG 4694 rail at the 12 o'clock position for optics and optronics, while optional MIL-STD-1913 Picatinny rails can be installed at the 3 and 9 o'clock positions via an adaptor without the handguard. An M-LOK interface is positioned at 6 o'clock, with additional M-LOK interfaces at 3 and 9 o'clock on the handguard. The charging handle folds, and a QD interface supports sling attachment.

Ergonomic elements include an adjustable and telescopic buttstock with a height-adjustable cheek rest, and compatibility with stocks such as the collapsible MP7 pattern and the HK416 A8. The pistol grip features interchangeable grip shells with black straps and an exchangeable trigger guard for winter gloves. A length-adjustable, foldable, and pivotable bipod is mounted, and a forward grip with integrated bipod is available among accessories. Additional equipment includes a quick-adjustment carrying sling with shoulder pad, an optional heat shield, and an optional shot counter. The handguard can be detached to reveal rail space beneath, expanding mounting options. Colour concepts include Black, Flat Dark Earth, and Sniper Grey finishes.

The HK421 first appeared publicly on September 12, 2023, at DSEI 2023 in London, where it was introduced as a reduced-weight evolution of the MG5 series, followed by further display at events including Eurosatory 2024 in Paris, MILIPOL 2023, and SHOT Show 2026. Compared with the MG5A2 infantry configuration fitted with a 460 mm barrel and weighing up to 11 kg in certain configurations, the HK421 reduces mass by two to three kilograms through shorter barrels and revised construction while maintaining the same 7.62 mm x 51 NATO chambering. The system retains key MG5 features such as the quick-change barrel, feed mechanism, feed tray cover with loaded belt indicator, and multi-surface sear engagement with carrier retention latch. Design objectives include maintaining interoperability with existing NATO ammunition, training structures, and mounting interfaces while increasing mobility for dismounted personnel.

Written by Jérôme Brahy

Jérôme Brahy is a defense analyst and documentalist at Army Recognition. He specializes in naval modernization, aviation, drones, armored vehicles, and artillery, with a focus on strategic developments in the United States, China, Ukraine, Russia, Türkiye, and Belgium. His analyses go beyond the facts, providing context, identifying key actors, and explaining why defense news matters on a global scale.