Things don't just happen, they happen for a reason. If the primer cup is not receiving impact or stress there's no reason the primer would detonate.
I saw the thread about impact pullers causing primer detonation. That's a different deal. Nothing strikes the primer cup, but I believe the priming compound pellet comes loose and impacts the anvil with enough force to detonate. I've used an impact puller myself for years and never had such a thing happen, but I'm thinking the whole thing over the last couple of days.
I think the chances of a loaded round detonating while being run through a body die is probably about ten thousand times less than when pulling bullets using an impact puller.
How about the way rounds powered by Cordite are made? Primed, straight-walled case receives its powder charge AND THEN the neck is formed. It's an assumption, I'll admit, but I think a very safe one: those cases are primed before the Cordite goes in. I think I'd MUCH rather do it that way than the try and prime cases already holding a powder charge---even if the powder won't leak out the flash hole.
I think it would take some doing to screw up enough for a loaded round to go off in a body die. I'm not sure I could figure out how to make that happen without some very deliberate stupid moves.
