I've used IMR 4064 for decades in various 308's with long (24'-27") bbl's, and have 15 lbs of it sitting around. It's always preformed well with the old 168, 175 SMK's using either 4064, RL-15. Currently my SBR 18.5" really works well w/the 169 SMK, and H4895. My long barreled 27" is still...