The blue nerf gun looks like it can be something pretty interesting and easily made into a blaster. As for the other one, it would appear that it needs a lot more work. It's kinda big and bulky, but it would work as a heavy blaster or like you said a Granade Launcher.
Just remember to keep in mind that all Star Wars blasters in the old Star War movies were based on WW1 and WW2 guns.
Other than that the blue nerf gun looks well on its way.