What is the correct name for a grenade launcher?

WWII & Korea had "Rifle Grenades" launched from the muzzle of their M1 Garand rifles. Vietnam was the first war in which specially designed "grenade launchers" were issued to the men. The M-79 Grenade Launcher was nicknamed the "Thumper" or the "Blooper" because that's the sound it made when fired. It was a break open (like a shotgun) single barrel, single shot 40mm grenade launcher (and not as effective as some historians seem to believe). In 1970 in Vietnam, the M-203 over and under grenade launcher was fielded. That was just as bad as the thumper, only worse: it was heavier because now the M16 rifle was attached to it and when you slid the front portion of the 40mm grenade barrel forward to load it, you had to keep the muzzle downward or else the whole round fell out of the weapon.

he means muzzle upward