Gun ammo ?? I would hardly call that an innocent site - guns kill!
If he is a gun sportsman I would expect he would get any supplies from a source or sources already known to him, or his gun club. I would have thought that on-line would be very risky.
Also, as the same thing happened to yourself, I rest my case.
Tell him of the millions of happy users surfing the web every day and night, encourage him to be a little more careful that's all.