Nice find. Surprisingly these silver war nickels are not all that rare in circulation, at least compared to silver dimes and quarters. I've got about 60 of them I've pulled from circulation in just the last 2 years. I think the fact that the mintage numbers were pretty high for some of those war years, coupled with the fact that many people don't realize silver nickels existed during that period, has helped prevent them from being completely culled from circulation which makes nickel roll hunting still interesting.
35% Silver War Nickels are a strange critter. The first US Coin to bear a "P" mint mark, they were made at a time (WWII) when silver was less precious to our national interest during the war than nickel, thus the metal content change. They also bear the dual-diagnosis if you will of having the lowest percentage silver content of any US silver coin, but also the highest silver content value per face value, right now about .94 ninety four cents per 5¢ face value, or $18.89 per $1 face value (20 nickels to a dollar). Consider that against 90% junk silver value per $1 face value of only $12.15, or even a Morgan or Peace dollar, at $12.99. And they leave 40% silver Kennedy Halves in the dust at just $4.97 melt value. It's even more than a $1 American Silver Eagle Bullion Coin, the world's most popular .999 fine silver investment coin. Yet? The other 65% of the metal make up of the Silver War Nickel, other than the silver itself, makes it a pain in the neck and thus very expensive to refine when melting, and as a result no one really considers them a decent investment, and you can pretty much pick up a roll of War Nickels for spot or a bit over, even on eBay.