The Fish case was an anomaly. The judge should have charged the jury that the caliber had nothing to do with the case, and the defense attorney should have objected to the prosecutor's "opinion" about the 10mm.
You're going to get stupid people on the bench and on juries. That's the way the system works. (or, in this case, doesn't work.)
I believe the prosecutor gets the last closing argument. If he didn't mention the "uniqueness" of the 10mm until then, then the judge should have addressed that idiocy during his charge.