Bill Jordan explains it all in his book No Second Place Winner. RichC got the gist of it. The most important thing to do is to ID your cases used for wax ammo so that they can never be mistakenly loaded as real ammo.
Why? Because the flash hole needs to be enlarged to almost the same diameter of the primer pocket to prevent backpressure from driving the primer out and locking up the gun (revolver).
When you fire a normal cartridge in a revolver, the case head is driven very strongly against the recoil shield, so much so that you can see the imprints of the heads on the shield around the firing pin. This force prevents the primer from backing out of the case.
Wax loaded ammo has such negligible recoil that the case is never forced back against the recoil shield with any force. The primer can then back out enough to drag on the recoil shield. If the primer pocket is loose to any degree, the primer can back out enough to prevent the cylinder from rotating at all. By opening up the flash hole, the back pressure against the primer is eliminated and the primers stay where they should when firing powder-less wax bullet rounds.
If, however, a case with an enlarged flash hole is loaded with powder and lead bullets, dangerous pressures can be generated due to the greater flame exposure from primer to powder.