The HK421 is a new 7.62 NATO belt-fed machine gun which made its debut at DSEI.
Based on the MG5, it has a hydraulic buffer which allows it to accept various buttstocks like this collapsible MP7 stock. It has also been seen with an HK416A8 buttstock. You’ll also notice the handguard module which can be detached to expose a Pic rail for accessories.
Offered in 13″ (8.3 kg) and 16.5″ (8.5 kg) barrel options, it features a 3-position gas block for normal operations, sustained fire, and suppressed. It can also be set on safe in any loaded state.
Heckler & Koch shared this photo of the HK421 on social media which shows the FDE version. They also adverstise a Sniper Grey version.