Once ages ago I heard a story like this, itself not young at time of telling, from a professor of physics. That story might have been set in Texas and did involve a handgun being fired into a telescope mirror which was not meaningfully damaged by the experience, but had it as a revolver wielded by a revivalist-type preacher who smuggled the weapon in during a tour to redress what he saw as a violation of God's domain.
It's been ages since I was in touch with the fellow who told the story, so I can't immediately confirm whether these were the same events. But the similarities are striking.
Alternatively, you could try contacting the sheriff's office in Austin to see if their records include a mention of the incident, but that information is probably protected.
