Michael right,

Most of these so called 300 million guns are locked away in kid proof safes - chances for a good guy who is packing a concealed gun and would want to get involved , so that would be a 1 -to- 300 million chance that would happen.

Slightly higher in states that do allow concealed weapons to begin with . The good guy guns are generally left at home for home protection and thats where the laws favor them the best.

Imagine if you will ?
Good guy gets involved in a shoot out with a bad guy to save lives - but a innocent bystander gets shot and killed by the good guy <-- he still could face murder charges even with the good Samaritan laws. Remember these thing happens in a few seconds at most - a good guy has gotta pull and fire in 2 seconds flat - I really don't think a good guy can do that ? ?