In addition to the problem of leading caused by bullets which are too soft for the velocity that was covered in Chris K's excellent response, leading in handgun barrels can be due to other causes. Rough bores will abrade lead from the bullet depositing it onto the rifling. It is eventually ironed into the barrel with each successive shot through the barrel.

Leading can also result from using a bullet which is too hard to expand under the pressure of the gas from the burning gunpowder. That prevent the bullet from obturating the gas which then pushes past the bullet. The heat from the gas burns off lead from the bullet and fuses it onto the bore. That leading will also be ironed into the bore with successive shots through it.

IIRC, leading towards the front of the barrel indicates a bullet which is too soft for the velocity generated by the load; and leading at the rear of the barrel indicates a bullet which is too hard to expand the bullet to obturate bore from the pressurized gas.

I use mainly lead bullets in target shooting. My low to medium powered loads are exclusively with lead bullets. I shoot jacketed bullets only in the higher powered loads. I normally have very little trouble with leading from my established loads.

Good luck,

John