Thats a good story Ray and illustrates the point perfectly. I would imagine that ammunition was given to your friend’s wife by the man in the shop who sold her the rifle. In many ways that makes it even more scary.
Have a look at the dimensions of the .350 Rem Mag. A very short belted magnum and then look at at the dimensions of the 7mm Rem Mag and the 8mm Rem mag.
Then imagine the scene “Hey Joe, your rifle is a Remington Magnum isn’t it? I’ve got these shells my friend gave me, he said they were for the Remington Magnum he sold last year…”
The .350 will chamber and fire in both the 7mm and the 8mm plus a lot of others like the .300 Win Mag, 257 Weatherby because they are all basically shortened and/or necked down versions of the .375 H&H Mag. They will all chamber and fire but no way is that big bullet going to get down that little barrel.
And its getting worse, thats the problem. There really is a case to be made for identifying ammuntion with a unique code like spark plugs are for example. All spark plugs look alike but put the wrong ones in the car and the effect can be much the same as chambering the wrong ammunition in a rifle.