The First Ray Gun toy! The Buck Rogers XZ-31 Rocket Pistol!

Although not actually a "ray gun", this is the first space-pistol toy produced!  In the comic strip (and novella upon which it was based), the rocket pistol fired high-powered projectiles!  The strip popularized the onomatopoeia "zap", which was the sound the gun made in the strip.  This toy pistol, manufactured by Daisy in 1934, cocks and when the trigger is pulled makes a loud "bang" (or "zap", as the box proclaims).
It's one of my favorite items!!