Home Forums Hunting & Shooting Hunting Rifles How thick of a plate of steel to stop hunting rifle bullets?

I made a steel spinning target out of 1/2" steel 3" diameter, for 22's. Was shooting at it with the Wife working in the yard 100 yards away and behind. She heard a bullet buzz by that was close enough to sound like a mad bee. That was the last time I shot the spinner! No more steel for me!
Virgil B.