Rifle Mounted Grenades are used in COD3 in any multi-player game mode. This is only able to be used when a player has a M1 Garand or the Karabiner 98k. These RMG's moved on to COD4 and were named the M203 Grenade Launcher.
Rifle grenades are fit over the barrel of a rifle so that when a blank is fired, the force from the combustion push it forward. Needless to say, they have low accuracy and range and are inferior to the grenade launchers of today.
They came back in Call Of Duty: WaW as an attachment for rifles. Im WaW though, you are required to complete the final Marksman Challenge. Note that the rifle grenade has a greater lob effect than the grenade launcher. Rifle grenades can only be equiped to bolt action and certain semi-automatic rifles in WaW. THe rifle Grenade is greatly hated and many players refer to it as the "noob stick"(Seeing as it is only a grenade on a stick.Duh!)
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