I bought a used Ruger Mach 1 semi auto. It wouldn't fire. Sent it back to Ruger and they said the damage was due to dry firing the weapon. There was noticeable damage to the face of the bore where the bullet seats. The gun was replaced at cost. Very cheap for a new discontinued model.
I'd be willing to bet that the firing pin stop had been lost.
For God so loved the world, that He gave His only begotten Son, that whoever believes in Him should not perish, but have everlasting life.
John 3:16 (NKJV)