Don't worry at all about your cast bullets being so hard that you create a dangerous pressure situation. I have never even heard of such with cast bullets (not to say that it isn't *possible*, but again I have never heard of it). The only factor that I can think of where the bullets themselves might give you any pressure problems would be if your bullets are greatly over-sized for your bore. Just mind all your reloading P's & Q's and you will be fine. BTW, I cast for hunting loads in my .44mag using max loads and I make my bullets as hard as I can by heating and water quenching.
Keep us up to date on how things go.