As a follow up, I've been reloading for quite some time now and the double charge I got last month was the first I've had. The equipment I use is pretty reliable and when something goes wrong in the process, it's pretty apparent. Still, I've added a station to the turret to check the powder level in each cartridge from here on out.
Looking at my shelf, I have some 500 rounds of .40 S&W sitting there and of course I have to wonder if there are any more surprises lurking in the boxes. The obvious solution is to weigh each cartridge which I started to do:
I suppose I could specialize in the PCC class at the matches for a while as the Hi Point is famously indestructible.