That is my kind of powder horn! I have looked through every nook and crannie of umteen dozen antique shops to find just one little gem like this. RTD, did it by any chance have black powder in it when you found it. On a couple of rare occassions I have found them with old BP in them. Most antique shop owners don't have a clue. I couldn't tell how old the powder was but it was fun to test fire the stuff and pretend I was using up the leftover reserves from the Alamo.
I'll always be a kid till they plant me.