Adrienne -
Musical instruments are frequently "played" to maintain their sound quality,
although that is a stretch when compared to firing a firearm.  However, since
the object appears to be contemporary by your description, it is a far cry
from the situation if it were a true historic firearm from the handcrafted
era (pre-1885).  I say, let the owner/donor fire it and "add" to the
significance of your piece.