That's the deciding factor. Load a cartridge with a pistol bullet and shoot it with a moderate load, say a 158 grain bullet and 46 grains of IMR 3031. Then check to see if a .358" bullet slides easily into the neck of the fired case. If it does, then you're set to go. The actual barrel measurement is unimportant, since the bullet will be sized to the barrel dimensions before it has travelled its own length in the barrel.

Neck release is another matter altogether. If you don't have enough neck clearance in the chamber, the bullet may fail to release, causing an enormous pressure rise with unpredictable consequences.