The general consensus is that as long as its stored in a cool, dry environment it's shelf life should be a very long time.

here's a quote from a post in another forum where someone wrote to Ramshot to ask about shelf life

Here is the response I received today from Rob Behr at Ramshot regarding the shelf life of Blackhorn 209:

"We are wondering that too. We have had samples from the first lot which we cannistered in 2007. We test it each year and so far have not seen a reduction in its pressure or velocity."

Rob