Does anyone here know if there has been a significant change in the burn rate of IMR 4064 in the past few years? I ask because I am noticing a big difference in 7mm-08 loads in my two Sierra manuals. Specifically: 4th edition (50th anniversary) 7mm-08 168 SMK Max load of IMR 4064 is 42.0 grains 5th edition 7mm-08 168 SMK Max load of IMR 4064 is 39.2 grains That is a pretty big drop in the max load. So what is going on here? Did the powder change that much? Different testing methodology? Or is the 39.2 grain max load a "lawyer" load?