Sources claim police are looking at the theory it may have been used to murder Reeva Steenkamp.
Officers are reported to be looking at the possibility Pistorius used it to break down the door of the bathroom where she was hiding or that the late model used it to defend herself.
City Press in South Africa claimed that sources said Miss Steenkamp's skull had been crushed.
The claims came as the athlete's best friend, Justin Divaris, told how he received a frantic call from Pistorius just after the incident.
The 27-year-old said the runner was crying and said: "My baba, I've killed my baba. God take me away."
Divaris said: "I said to him, 'What are you talking about?'
"He then repeated himself – 'There has been a terrible accident, I shot Reeva'."
Members of both families spoke yesterday, with Pistorius's father Henke 59, saying he had "zero doubt" the fatal shooting was a mistake.
Ms Steenkamp's father Barry said he bore no animosity but added he was struggling "to find some reason why this happened to our lovely daughter".
Ms Steenkamp's funeral will take place tomorrow, the same day Pistorius is back in court.