I find that my SKS's shoot best with powders in the H322 burn rate range. About 28.0 grs with the 123 Hornady FMJ. Another good load is a near full case of H4895.
Fast pistol powders do not produce enough gas at the right pressure at the right time to reliably cycle the action. However, 2400 is on the slower side and I have heard of success with it with 15.0 to 16.0 grs.