Unfortunately, this coin can not be checked by weight. Both the standard cupronickel alloy and the copper-silver-manganese alloy of the war nickel result in a five gram coin. While the war nick tends to oxidize darker than the more common cousin, this is not always the case. If you have evidence it may be the wartime silver alloy, by all means please share, because the alloy can not be determined by pictures.
Time for more coffee.