I realize that black powder is not really Krag related, but I also know how smart everyone is on this site.

My brother-in-law found an old pound of Dupont FFFFg powder in his mother's house buried in a closet, and brought it to me because he knew that I would know what to do with it.  My guess is that the can is 40 years old or more.  As far as I could tell, it was unopened.  I opened it and checked it for any signs of degradation... and found one tiny clump at the top that broke up as soon as I touched it.  I poured a small amount (about 50 grains) into a pan and did a burn test... and got a nice POOF out of it. 

My questions are this:  Is this still viable powder?  What could this be used for?  I'm planning on loading some 45/70 in the near future.  Can FFFFg be used for 45/70?  I also have an older replica 1858 Remington ball & cap revolver, can this powder be used for that? (I used to use FFFg, and now I use Pyrodex P).  If this powder is not safe, then I'll destroy it.

Any help would be greatly appreciated.