Even though softish steel jackets are used in some military arms quite regularly, they do accelerate the wear in the bore.
Considering that match shooters in High Power can tell when their barrels 'go' from shooting just guilding metal jacketed bullets, sometimes in a matter of only a few thousand rounds, and that I have personally shot over 3000 lead bullets through one 22 Hornet I had in only a few years, I dont want steel on steel. Turning solid copper bullets may be OK, it is soft enough to give with the rifling impression, if the rifling isnt too deep, but pressures will go up I expect. Brass is another matter, it can be fairly soft to pretty hard, so dont grab any old hunk of yellowish metal to turn some.
Another thing to consider is that there may be some legal restrictions on the making and using of 'body armor piercing bullets', not sure, but I remember there was talk about it some time back. If there is not now, its likely to come back around.