[Unclenick]

It can last over a century if the storage conditions are right, but since it came from a Garage sale, you don't know what it's storage history is? In general, if powder is breaking down it will smell acrid. There is a normal solvent smell, but something that reminds you of the smell of car batteries is not good. Also, there is a fine red dust that appears resembling rouge or powdered rust when breakdown goes far enough. Toss a tablespoon of the powder around on a white sheet of paper and see if any red powder shows up underneath it?

If the stuff is breaking down, sprinkle it on your lawn as a high nitrogen fertilizer. If it is not, and your load felt hotter than the military hardball load that 5 grains of Bullseye mimics (which is warmer than commercial: 390 ft-lbs, vs 350 ft-lbs), just knock it back to 4.2 grains (an old target standby load) and see how it does then? A chronograph will let you compare it to commercial ball. In that instance, same gun, same chronograph, same test conditions, you can compare it and get a rough assurance, since that powder was once used for military .45 ACP loads, that it will be within reasonable pressure limits when loaded to the same velocity as commercial ball.