I believe I saw an estimate that there are 700,000 instances of firearms used in SD annually (fired or not). If both those numbers are correct, it would be an average of 396 years before any individual would need a reload in a SD situation.
Basing decisions on such statistical conclusions is what leads people to build homes in 100 year flood zones. They rely on the fact that such a flood has already happened to establish that there home is safe for the foreseeable future. They get shocked when they get flooded out, and even more shocked when it happens again.