You can pust a cast bullet as fas as you want.
BUT if you push a case bullet too fast you will have poor accurey and spend lots of time cleaning.
The speed that you can scencably push a cast bullet depends on the alloy that the bullet is made of and if the bullet has a gas check or not.
In a rifle I push HARD bullets with gas checks at 2300 fps and get little leading
I have also seen a soft pistol bullet pushed at 1200 fps and it leaded the barrel so bad that the rifling was not visabile.
IMO don't try to push a cast bullet at the 3000+ fps or pressures may build quickly do to leading from the shot before