Russia's naval special forces spend about as much time underwater as they do above it. As such, these aqueous commandos typically are required to carry at least two firearms, one for land assaults and a second outfitted for underwater combat. But this amphibious rifle is equally effective in both environments.
The ADS amphibious assault rifle is built specifically for Russian combat divers by the state-owned KBP company. It's based on the venerated A-91M bullpup assault rifle platform and fires 5.45x39mm M74 rounds (the same used by the AK-74) when on land. It also accepts an underbarrel GP-30 40mm grenade launcher and a host of optical sights.
The genius of the ADS is that it utilises the same calibre round in both mediums. Earlier models, like the ASM-DT, needed a longer, waterproof cartridge for submerged shooting which necessitated that troops carry double the ammo and adjust the rifle's receiver when switching between the two. The ADS, on the other hand, sidesteps that issue by utilising the single 5.45mm x 39mm cartridge. The underwater rounds, known as the 5.45mm x 39mm PSP, do feature longer slugs designed to move through water rather than air, but are packed into the standardised casing. This allows special forces to simply swap out magazines when moving from one environment to another and eliminates the need to carry a second rifle.
The ADS has an effective underwater range of 25m and is about as as the AK-74 it is meant to replace. The ADS is currently undergoing extensive field testing by the Russian military for use in counter-terrorism and security operations. [Motherboard - KBP - Wiki]