I agree that the long throat will add to the hangfire problem. All of the CZ magnums have long throats. My earlier reduced cast load attempts with my 458 CZ resulted in the powder being "blown out" while the projectile transversed the vast expanse to the start of the rifling (it also got stuck in the rifling). Weird thing too - I'd used a filler but it wasn't blown out of the case at all and you could see where some of the powder underneath it had tried to light (it was pale in colour and clumped together). I was using magnum primers too.

2208 is relatively fast but 100gns is alot to try and fire up.

One other comment - cases with pronounced shoulders are easier to light up the powder and less likely to hangfire as easily. The shoulder acts as a restriction to powder forward movement and is also a pressure reflection point to keep the flame where it is meant to be. In a straight walled case with reduced loads I'd imagine the flame must run forward and go out if there's no powder at the end of the path.