Pure WW will obturate just fine in a MZ. The same as it does in a 45 Colt or 45-70 in a rifle. I shoot a bunch of WW in 45 Colt and 45-70 with a 300 or 400 grain bullet at 1200-1400fps. With perfect obturation of WW.
Thor sends out sample packs for one reason. They also realize that proper sizing of their bullet is much more important than the alloy of the lead. It matters not how soft your lead is if your bullet is not sized properly.
I have shot a bunch of cast bullets in MZ's and CF rifles. Accuracy, leading, and proper obturation always comes down to one basic variable. SIZING. With lube being number 2. And alloy a far distant proerty unless you ar really pushing it hard. Then harder lead is better, not worse. And a GC is necessary if you really speed them up. Tom.