Now I'm not a bulletsmith, first of all. I did take some advanced chem in school, so this discussion is mostly theoretical.
It'd be difficult, because the melting point of silver is almost 1761ºF, while Lead is 600ºF.
You'd need molds made of steel or chrome or Iron, not to mention a good heat source. You'd have to make sure the mold got hot enough, otherwise the silver won't flow properly; making a cruddy bullet. Getting the silver isnt hot enough, because if the mold is colder, the silver will solidify in clumps when it hits the mold.
Silver is also not as malliable as lead, so rifling won't get a chance to really grab it, so your silver bullet would probably not be very accurate.
You might want to consider alloying the silver with some other, softer metal to improve accuracy, but this alloy's effectiveness on werewolves might be lessened.
Now I wonder how coating the silver bullet in copper or lead would do, but this gets me out of my comfort zone of theoretical discussion, at least without trying it.
Which might be fun someday.