The 139 light mag's out of my 15" Encore are right at 2560+- some so if you add 300 to that for a rifle it's knockin at the back door. My handloads are at 2600 with N550. I don't think you'll find out what the powder is either as they state that it's a special bulk that they buy. I did pull one and measure it but don't have my data here at this time. They seem to shoot pretty good though, and if I were stuck with no handloaded ammo that's what I'd buy.