The 23-year-old TV star is so "gun crazy" his father, legendary rocker Ozzy Osbourne, worries Jack will end up hurting himself.
He said: "Jack is gun crazy. Over here in the US you can buy real guns. I have this horrible thing - I can see this movie in my head where he's messing around and shoots himself in the foot."
Ozzy also fears Jack - who has spent time in rehab for alcohol and drug addictions - could pull the gun on someone else if they pose a threat.
He is quoted by Britain's
newspaper as saying: "I said to Jack, 'If someone got into your house would you be willing to use your gun?' He said, 'Sure.'
"I said to him, 'You know what, Jack, when that burglar came into our house in England I had him in a headlock and the thought went through my head that OK, I could kill this guy but could I live with the fact I took his life? No. What if I maimed the guy or pushed him out the window and broke his leg? All these scenarios went through my head.' "
However, Ozzy says his wife Sharon Osbourne has a far more laidback approach to Jack's penchant for violent weapons.
He added: "Sharon goes to me, 'Oh darling, he's been surrounded by guns all his life.' But there is a difference between an air rifle and a 45-calibre pistol."