Not trying to be a dick, but did he take the rifle to the range before season with that batch of primers? I used to use Musket caps on my Remington 700ML before converting to .209s. Well, one year I bought a new tin of musket caps and when I was sighting in they wouldn't fire. The whole damn tin was bad. I'm not sure if they got spoiled in transit or what, but they WOULD NOT ignite a load.

Can't leave anything up to chance with muzzleloaders. I hate that your son had one walk on him--that hurts.