9,3X57,
I think it’s a grand cartridge that offers plenty of performance without a lot of fuss. The factory rifles I know of are Heym Express and Mauser 03, plus a few “semi customs” from smaller makers and CZ. Hopefully Winchester, Kimber or Ruger will chamber sheep rifles in 404 Jeffery

RWS, Norma and Kynoch offer readily available ammo and today it is loaded to similar performance as 416 rem and 416 Rigby. 404 Jeffery fits nicely into a stretched standard 98 or an action suitable for 375H&H.

Supplies of brass, dies and bullets are better than in a long time

Johan