Mostly lead. If you check the websites of the various makers, you'll find suggestions along with velocity limits. The plated bullets won't lead, so, in many cases you can drive them faster than lead bullets. In some cases, like 9 mm, you can, use jacketed data, but you can slightly reduce charges and get the same velocities.

You didn't mention calibers, but I find a taper crimp sufficient with my plated revolver loads. You're not likely to get the recoil that will cause the bullets to move forward.