
If the revolver was fired alot then sat they sometimes leave a build up on the firing pin which will shorten the stroke of the hammer thus not extending the pin all the way. If the primers are a deeper set primer it will not fire. I suggest a through break down and cleaning.
I bought a Taurus semi model 917 9mm and had a similar problem, turns out the oil they use on new guns hardened behind the hammer wall from sitting had to disassemble the gun and scrap the material off it was like a waxy build up.
Just a thought, I am by no means a gun smith but I do own a few. I also have 3 Taurus's and they have a lifetime warranty any Taurus dealer will ship gun to the Taurus factory for service. If your dealer won't I suggest a phone call to Taurus Customer Service
Phone: (305) 624-1115
Fax: (305) 624-1126
Mailing address
16175 NW 49 Avenue.
Miami, FL 33014