I look at picture after picture and find some with the projectiles up and some with the projectiles down in the ammo racks, when I can find pictures with ammo in the racks at all. Is there a definitive answer or can ammo be stored either way, projectile up or down?

This might give you a basic idea.

https://forum.warthunder.com/index.php?/topic/206921-pz-iv-ammo-rack-locations/

Thanks for the link. It looks like I'll be storing the rounds with "the dangerous end down", which won't look as cool, but will be less expensive and easier to model, and even scratch build. Most discussions of Pz IVs are about the long barrel versions, so I have to be very careful not to use the wrong references.