Purchasing coins mostly made of silver?

Well if I was able to purchase them based on face value, for example if old nickels were made of mostly silver... would I then be able to sell them based on their weight in silver? Would this be a good investment?

First of all, old nickels are NOT made mostly of silver. During WWII, they were 40% silver.

But if you could buy old U.S. silver coins at face value, (i.e. a silver dollar for a dollar) that would be less than the current value based on their silver content. But good luck finding a sucker willing to make that sale.

Why would you want to? Why wouldn't you sell them as coins to a dealer for their collector value?

Of course it would be a good investment. However, dimes through halves with silver disappeared from circulation in the 60-70's, and the last "war nickel" I have received in change cam about 25 years ago. The one exception I would make would be bags of half dollars that you can get from banks. I frequently find 1965-1969 half dollars in them, and they are 40% silver. Most people do not know they are silver since they have the clad looking edge. I would try that if you want to do this.