Are all silver half dollars the same?

A very common term in the metals business is "junk silver".  Many people walk into the shop asking for our price on junk.  Junk silver is Quarters, dimes and half dollars prior to 1965.  There is a bit of a fine line however, with some of the older coins.  The barber, Liberty Seated, and the mercury dimes. Some of these coins can have value up and above the silver content.  Old U.S. silver coinage is an excellent way to invest in silver and our far "right-wingers" like the fact that they could possibley barter with these coins, should the dollar crash(pretty extreme i know, but we all have our convictions).
There is a type of junk silver that is overlooked.  The 40% kennedys.  These coins were minted from 1965-1969 and have less silver than those minted in 1964 and before, but they are still a great option for investing in silver.  Dealers often consider these to be the "redheaded stepchild" of silver, and often give these coins away in terms of pricing.  Kennedy halves in the 40% variety are a legitamate way to hoard silver, but there is a drawback and that is bulk.  If an individual is investing 100k in junk silver, they will have twice the bulk with 40% halves because they are the same size with roughly half the silver.  If you are selling old silver coins, we are very interested in your 40% halves.