The tracer compound is in the base of the bullet, covered by a very thin piece of copper. When you look at a typical FMJ rifle bullet, you'll see the lead exposed base. But with tracer rounds, there is a little cap down there covering the tracer compound... What that stuff is, I don't know... Phosphorous, perhaps?
I don't know if you could carefully pry off the little copper dish that's placed there to cover the compound. If you could, makes me wonder how much the dish and the compound weigh, leaving you with what bullet weight.
I won't shoot them myself--my .223 is a T/C Contender. I have no idea what they can or will do to a barrel.