There's a big difference between numismatics (coins valued for their rareness and excellent condition) and commons or 'junk,' which are valued for their metal content. The advantage of 'junk silver' is that it is readily recognized and thus, easily traded. There is at any time a straight multiplier to face value, which simplifies transactions. Let's say it is 20; that means a US silver dime (pre-1964) is worth $2, and a quarter $5. If it is 22, then $2.20 and $5.50 respectively. Bullion is harder to validate, thus harder to exchange. But still, better than nothing.