Rules of thumb for maximum velocity:
•Gas check hard cast bullet: maximum 1700-2000 fps
•Plain based hard cast bullet: maximum 1200-1700 fps
•Plain based soft cast bullet: maximum 800 - 1000 fps
this is assuming a good condition, clean bore.
Some rifles will do better, some not. Bore condition and bullet fit are the biggest factors.
Bore preparation: Before you start with cast bullets - leading can be prevented by giving the barrel a good scrub with copper and lead solvents before shooting cast.
Barrel Break-In: With a new rifle or barrel, break in the barrel with 20 or more jacketed bullets before shooting cast. After break-in with jacketed bullets, switch to cast and there will far less initial chance of lead fouling.
Cast Bullet Sizing: Cast bullets need to seal the bore well to prevent gas cutting, A cast bullet is normally .001-.002" larger than barrel groove diameter.
Barrel Condition: Barrels that have rough sections, excessive pitting, rust, or damage may suffer excessive lead fouling with cast bullets. Jacketed bullets are likely the best bet for these barrels.