just about anything from IMR3031 to Varget and R15 and nearly anything in between. A lot slower and also the op rod is vulnerable to having bent with the port pressure timing. 4064 can be a fav. In my M14 rifles I utilize it and 4895 and AA2530 in addition. I generally continue to keep the R15 for my M40 bolt rifles. unconventional Recoil or sound