Who makes a 24 gauge shotgun?
Not a standard gauge in the US, although ammunition is still loaded in Europe. Some Italian and Spanish shotguns were imported in the 1970's.
i used to have a tecni-mec (rizzini company connection, Italy) o/u 24 gauge which i ordered directly from the company in Italy in 1990, sold it in 2001.
it was about 6.5 pounds, 27 inch barrels & i liked it a lot, even won some bets with it in bird hunting camps because people refused to believe it was really a 24 gauge. my best friend talked me out of it in 1991.
i am currently in the process of buying a falco (Italian also) sxs 24 gauge with about the same weight & barrel length as my old o/u.
the only ammo i know of is made by fiocchi & imported by fiocchi of America.
i know of loads with #5, #6, #7 & #8 shot sizes, 9/16 oz. in a 2 9/16" case & 2 drams of powder, about the same power wise as a low power 28 gauge.
i you could hand load for it & get 7/8oz of shot & 2 1/4 drams of powder you have a much more effective loading just like a light 20 gauge load.
tecni mec & falco are the only two companies currently building the 24 but i am pretty sure there are more in Italy, a country in love with small gauge shotguns.