Jack didn't know what was happening. He came back to life with a painful gasp and sudden surge, hearing the Doctor's denial. He wasn't thinking, wasn't even feeling, just shoved up onto his feet and ran toward the Master, toward the enemy, forgot about the gun, forgot about everything.
He dove into the TIme Lord, hands around his throat, knee in his stomach and strangled him with everything he had, choking the life out of him and nothing in his eyes but animal fury.