Smell is the first indication of bad powder. If it smells acrid or harsh, instead of having the normal powder smell, it's going bad.
A second test is to pour some out on a piece of white paper. Look for any reddish dust, but be careful not to breath any if it's there, it's poisonous.
If there's a red dust there, take the whole can outside and sprinkle it in a grassy area or in a flower bed. It will decompose and add nitrogen to the soil.
"The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza
Baby Jesus cries when the fat redneck doesn't have military-grade firepower.