If you can eject a loaded round from the chamber, it's not too long.
With cast bullets, pressures don't ramp-up like copper jacketed bullets.
For reference you should get Lee's Modern Reloading #2, and read whats stated here;
http://www.lasc.us/FryxellCastHollowPoints30-30.htm I have driven hard cast bullets faster than jacketed without leading, but the best accuracy comes from air cooled wheel weight (BHN 13), gas checked & lubed at .310 (this just applies lube and sets the gas-check, it doesn't size the bullet), with a light crimp to get rid of the case mouth belling.
And I did take Fryxell's advice on powder too, 26gr of H335.