Shattering does sound like compatibility problems, however your annealing schedule could be the problem also (breaking in half).
When you turn a kiln to a specific temperature it drops fairly fast to that temperature, especially with the door partially open. Thermodynamics tell us that any container of heat seeks to equalize with the mass of air around it as fast as possible. The bigger the difference of outside temp to inside temp in your kiln, the faster the drop of temp inside the kiln. This is exactly the opposite of what you do when annealing. To anneal glass you have to slowly drop at the high end of your temperature by turning the kiln down very slowly in small increments. Mary Beth is right, no more than 100 degrees an hour is probably what most people use and that means around 1 1/2 degrees a minute. It doesn't mean you are holding at 960 and turn the kiln to 860 and leave it for an hour. Your kiln will drop to 860 in a matter of minutes. The inside of the bead will still be 960 and the outside will be 860 (an exaggeration, but as an example). A bead has to cool the same inside and out, because glass contracts as it cools. If the outside is cooler it contracts more than the inside and thus splits in half to relieve the stress. So, your best schedule will be to turn the kiln down perhaps 50 degrees and wait a half hour or 45 minutes, then another 50 degrees, etc., until the kiln is below 800 degrees. A lot of people still cool at the same rate of 100 degrees an hour down to 600 or even 400 to prevent thermal shock to beads, especially if they are larger. However stress cracks due to annealing won't happen below around 800 degrees.
Another thing you might want to consider is that your kiln controller may not be reading the correct temperature. It might be saying 960 when it is only 860.
The other possibility I was wondering about is whether you are allowing your beads to get too cool during the beadmaking process. Perhaps the bead is actually cracked before you put it into the kiln.
Just some things to think about.
Good luck.
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