We have posted about these quick detach M203 launchers before when G&P sent us updates, now both long and short models are in stock right now at eHobby Asia. These use 40mm gas shells with the "Skull Frog" logo engraved on these. These can fit full scale M4/M16 airsoft guns and also the G&P standalone grenade launcher pistol.

G&P Skull Frog Type QD M203 Grenade Launcher (Long, Dark Earth)

G&P Skull Frog Type QD M203 Grenade Launcher (Short, Dark Earth)