It's mostly in the "Shot String". First off, PRB should not ever give you the opertunity, if your equipment is up to snuff. Most target loads are not very hot or fast. Pretty much the same on Sabots but you do see posts about plastic deposites. That leaves conicals and you can run into leading on these but again, how many rounds does one shoot at one time and afterwards you go home and do a complete cleaning. It's hard to lead up a clean, seasoned bore. The only time I ran into a leading problems is on a pitted bore that tore up my patches and started biting into the soft lead. If you stop and think about it, it makes sense.
Be Safe !!!