anything at all from IMR3031 to Varget and R15 and just about anything between. Significantly slower along with the op rod is liable to getting bent from your port pressure timing. 4064 is really a fav. In my M14 rifles I utilize it and 4895 and AA2530 in addition. I commonly preserve the R15 for my M40 bolt rifles. AR15.COM is the globe's greates