I did take the time to research the issue before I spoke, and found a couple of credible sources that put the boiling/decomposition point of potassium nitrate at 400C/752F. Here's one of the links:

PubChem, US NIH

This seems to conflict with the info you posted, and at the moment, I have no way to resolve which, if either, is correct. I suppose that one of us could run a sample up to temperature and see what happens.

Annealing is linear with time, but cubic with temperature. If you want a quick anneal so that the mouth of the case can be done before too much heat reaches the case head, then 800F is a good choice. That is where I run my bath. You can anneal below that temperature, but it takes much longer.

Last edited by denton; 03/05/19.

Be not weary in well doing.