Bear skulls really don't shrink much.
I think that I've had them shrink from 0 to 2/16", or ever so slightly more (of course, I'm going by memory and I'm 61, LOL!).
However, the potential for a greater discrepancy is there, as it also depends on several factors such as:
How clean the skull was when it was measured fresh, how "tight" or how strictly it was measured, what was used to measure it, if any fractions were rounded off, who measured it, and where and for how long will it be drying (60 days is the minimum but I've waited a few years sometimes because of where I live).
And make sure not to lose the little teeth in the upper front.
I've been "playing" with bear skulls a long time.