They apparently were not concerned about the possibility of the shot sticking in the bore, as they stated that loaded with the proper wadding that the shot could cool down completely without setting off the powder charge. I assumed that they were still able to fire the shot out of the bore. It probably caused increased wear on the bore.
What they said was the heated shot when cooled would no longer fit in the bore. I have never tried this, but I don't think they would have said this if it wasn't true.