The 40mm M397 cartridge is a low-velocity "Jump-Up" fragmentation grenade fired from 40mm hand-held grenade launchers such as the M203 or M320. The grenade has a delayed high explosive assembly that is ejected from the grenade on impact and detonates five feet above the impact point. This creates an airburst like effect that allows for better distribution of the grenade's fragments.
A similar Russian grenade, the VOG-25P, is used for the GP-30. It also uses a small charge to eject the HE assembly in the nose into the air before a delayed detonation.
After the release of Close Quarters DLC, all players now have access to this ammunition type for their M320/GP30 launchers. Instead of detonating on impact (40mm Frag), the projectile uses a 3-second timed fuse. The blast and damage are comparable to a hand grenade, and kills are awarded as grenade launcher kills despite firing a grenade. The LVG inflicts little to no striking damage and cannot break walls or cover of decent protection. The LVG grenade has a lower velocity than 40mm smoke or Frag, but flies almost twice as fast as thrown grenades. Its blast radius is shorter than that of hand grenades, but has a larger blast radius than 40mm Frag grenades.
40mm LVGs have a glowing orange "live grenade" icon like hand grenades, making them useful as a visual deterrent. Earning kills with the weapon often means firing into crowds where visibility and movement are reduced, attacking distant targets so they don't have time to react, or placing the grenade around corners ahead of moving infantry.
— In-game description
The 40mm LVG returns in Battlefield 4 as an ammunition type for the M320/GP-30, and is the last gadget unlocked for the Assault kit. It functions in a similar manner to its Battlefield 3 counterpart, retaining its large splash damage and hand grenade like nature, but the grenade's manner of detonation is somewhat different. The grenade has a five second timer if it never comes into contact with a surface, otherwise it will explode after bouncing twice if it hits a surface within about 20 meters, or will explode after one bounce if it hits a surface past 20 meters.
Also, the grenade is now capable to doing 25 damage on impact with players, and as the blast of the grenade does only 80 damage, a direct hit is necessary to kill a player with one shot. Due to the nature of the grenade, this is fairly difficult to achieve, so the best way of getting kills with grenade is launch/bounce it into groups of enemies that are already injured.