I, my son & a brother all have Brno 304 Combinations. Good, practical field guns. For my own, I use 4831 starting loads for 7 x 57 from a reliable manual. I don't crank it, and use Norma 175 gr bullets to get some mass, and for the .283 diameter, hopefully keeping the pressures reasonable. If you have Norma components, their manuals list loads for both 7 x 57R and 7 x 65R
My small game load is a lee 145 gr cast bullet ,wrapped in Teflon Gasfitters tape, over about 7 to 11 grains of Unique, Herco, or Universal. I top the powder with a pinch of teddy bear guts (dacron). Other powders in the same relative quickness range can also be tried. To save my 7 x 57R cases, I use .303 Brit cases, fireformed on the first loading. They get a bit pregnant looking, and you have to avoid case separations if `the brass was used in a loosy goosey Lee- Enfield. 30-40 Krag might be a better choice of case.
Don't use .303's or Krag cases in full power loads. I have heard of using .444 Marlin cases, but the ones I tried sized OK to 8 x 57R, but wrinkled on the next step. Maybe some annealing?
Waidmanns Heil