I ran up to 61.9 gr N570 in my prc when barrel was fairly new. After a few hundred rounds max is 60.8, still running 3100 w/ 156s. There's a good node @ 3080 so that's where I run it 60.5. The early description of n568 was essentially short cut N570. Whether this is true or not, I don't know. N5XX series powders burn very hot, excellerate throat wear and carbon foul really badly. They are(minus 560)very temp insensitive, and usually make top velocity. There's pros and cons. Clean your barrel often! And get a teslong bore scope to keep an eye out for carbon rings in the chamber neck and throat.