In extreme temperatures, I can see the brass contracting and expanding, but I don't believe it would be any more than a few thousands if that. The more likely hood would be the balls sticking.
I'm guessing that the holes for the ball bearings are a few ten thousandths smaller than the ball it-self, and I do believe that in extreme cold, the brass would contract faster than the ball bearings, causing them to act like they were stuck. On extreme high temperatures, like in the trunk of a car on a 100 deg day, the brass would expand more then the balls, and then trying to use it you might force the balls out.
Just my opinion.
I tried to make a smaller head for 20 ga., not so easy, everything is in relation-ship to the I.D. of the brass head, along wih the O.D. of the inside aluminum tube and O.D. of the balls.
