Howdy everyone! I will try to answer all the questions asked and provide any further clarity to the situation. Thanks for all your comments, some of which prompted me to re-think what happened.
This was day 2 and the 3rd stage of the day. The guns had been cleaned the night before, so had been fired for two stages prior, and loaded same as the rest.
Bullet was not found and did not penetrate the boot, causing only a tear.
Right foot, big toe.
At the end of the stage all caps were cleared and guns checked as unloaded by UTO. After this I notified the PM I was attempting to discharge that particular cylinder.
This is where I made a crucial error. I recapped to clear the chamber, then set it down. All guns were on the table at this time. I decided to get my backup pistol to finish the match and I began to reholster the pistol to move the guns to my cart. I neglected to clear the cap from the unfired cylinder! While the cap may have been fired, it was still on the nipple, maybe contributing to the discharge.
Phantom - There was no UTO present at the time, not an unusual occurrence when clearing a cylinder between stages. My negligence entirely.
Bullet was chambered, no squib.
All that said, I still believe the hangfire was initiated when I changed the attitude of the gun. While it was 15-30 seconds after the cap had fired, I obviously did not wait long enough to deal with the hang. The low velocity of the bullet was probably due to a poor load (insufficient compression), fouled nipple reducing sufficient ignition, high humidity, or all of these. I will of course keep all of this in mind when a FTF occurs again. Luckily, I am still around to live and learn.
Thanks for all your comments and concern.