I bought quite an array of powders a couple tears ago from a gun shop that closed down and there were 3 lbs of Win Magnum powder. is this stuff for 300 win mag? FS

It's a discontinued powder that is similar to the current 780.

According to a few powder burn rate charts that powder is between H4831 and AA3100. 780 shows next right after those. So it's very close to the 780. Just work up your loads carefully to you get to see how it reacts.