I use Retumbo in my Ultra's 300 & 338 . It has given top velocity in both . It is , as far as I can tell , very temperature insensitive. I can easily drive a 30 cal 180 gr. Partion at 3300 and a 250 338 cal Partion at 3000 . In fact I have to keep throttling back , the 250's were running 3060 in the 338 ultra no sign of presure but I'm sure it was over so I backed down to 3000. I plan on trying it in my 300 win and 7MM Rem mag. Good hunting KH