Being a very amateur historian I was reading up on the old M-79 grenade launcher. As one does. (I had a lot of fun shooting these during my Second Class cruise as a midshipman in 1975.)
The odd fact: the buckshot load for the M-79 was 20 pellets of 24 grain "metal" balls (subsonic too). I put metal in quotes as that's what the specs said and perhaps the implication is that they weren't simple lead balls. This appears to duplicate one of the more common 20 gauge 2 3/4" loads today. The M-79 was only 6 pound weapon so the relatively light load could be recoil related but it's really not very impressive.
The question: To those who were there or have better data than I, did these historically work? The M-203 of course obviated the need for a close in self defense load of this type of loading. Still, imagine being in a fight with a single shot 20 gauge extractor only shotgun.