If he is so smart and cunning why didn't he test his MacGuffin

Small scale and multiple attempts aren't always possible.

Some stuff doesn't work small.

Also extreme hubris.

>>51580513
>extreme hubris
But he's the Socrates of 40k. "I know that I know nothing" and stuff.

>>51580626
He flipped on his switch during prospero's burning and first drop into planet of sorcerers.

Talk and thoughts are cheap. Gotta get shit done or obtain methods of getting shit done is his new motto

He had to do it fast because he was afraid he'd be the next guy to turn into a balloon of meat and rape.

Also how would he have known or known to check if it turned people to dust?

>>51580825
By casting it on like 10 legionaries first?

>>51580475
Chaos ever evolving.
Who know if the ritual would even had effect the second time it tried ? The source of the mutation could have adapted, or something.

>>51580475
Cause the plot demands it.

>>51580475
Its a macguffin, it runs on unobtanium. Shit only works once.

In universe, its a large and fucked up ritual that interferes with an actual chaos god of magic's curse and the most psychically powerful primarch, held together by a rapidly fracturing coven of sorcerers on a world of chaos. Probably only going to get it together enough to try that once.

>>51586828
>Shit only works once.
Well its canon(BL canon) that it happened at least twice. But its believed to have happened on a smaller scale several times since then.