Just shake it up so its consistent. Its all good!I'm always wary of open powder.
"On yeah, gramps just used to take all the powder off his bench at the end of the day and dump it in here. Sure to be a good mix. "
40 years is old but not out of the relm of use. Open it and smell it, then pour some out on white paper and look for rusty looking particles and make sure all grain look the same. (like all are sticks and not mixed with ball.)You realize that DuPont quit making IMR powders about 40 years ago, right ? If you bought it for the antique can, you did alright, bit I don't think it's wise to load with that powder.