Yes, it does melt. Just take a tuft of it in a pan and touch a lighter to it. How much is left? And it all blows out the barrel.
Yes, if you stuff a case full of it then you could create a small plug of melted goo, but, that's not how it is used. If you compress it you are doing it wrong. You want it to be 'fluffy' inside the case. Look up the sticky on fillers.