 Ammunition used in the spigot-type Japanese grenade launchers often has paper bullets and can be identified by the staked primers.The 6.5 mm Japanese round was criticized as being under-powered in comparison to American and European military cartridges such as the .30-06, .303 British, 7.92×57mm Mauser, and 7.62×54mmR.For this reason it was later replaced by the more powerful 7.7×58mm cartridge.