I kind of have to go with Keith on this one...

I think you dry holed her.. You loaded with out powder. Give me a nickel for each time I done that he says..

209 primers are pretty strong. When you ignited the first one, that was enough to knock the projectile off the little plastic/polymer sub base. If you tilted that barrel even slightly to the ground as you removed the primer or wondered what had happened, that bullet would have fallen out. Next time there look in the grass around where you stand.

Or the primer might have been enough to simply blow it out the barrel a very shot ways. Primers really do have a lot of power.

When you removed the breech plug and saw the burned powder... what you were looking at is the burned powder and fowling from all your other shots. I am kind of surprised the little plastic sub base did not fly out on the next couple primers, but it might have been wedged in all that fowling..

That is my guess as to what took place...