Regardless if it is lead or not, it is still being shot through that hard steel barrel at 1300-1500fps. Will it wear down the rifling on the first load? No, but it will wear the rifling down over time and use. How much wear?
I wouldn't do it either, but NOT for the reasons you stated! You wouldn't live long enough to see any wear in a bbl! All he would get is poor patterns...
Even jacketed bullets don't wear out a rifle bbl when shot at high velocity, let alone lead at low velocity!!
Drilling Man