Big Daddy-inspired pistol by Amanda Jean Lopez.
She was inspired by GirlyGamerAU, who made these Bioshock and Bioshock Infinite-inspired pistols:
GirlyGamerAU/Nerfenstein has actually made a huge number of custom Nerf pistols based on Akira, Blade Runner, Portal, and much more:
And finally,Amanda Jean Lopez's site is full of steampunk designs, including this homemade Tik-Tok from Return to Oz:
*Buy Nerf guns at Amazon.