Start with a good bullet shape. It's just like drawing a triangle with curved lines. Don't forget to add a lip to the front side of the body.
This is where the rays come out. Simply draw a circle opposite the body. Be sure to leave enough space in between for the next step.
In between the body and the emitter, draw 3 thin ovals of different sizes and join them together with a super sophisticated carbon rod (or just a stick if you'd prefer)
Under the body, draw a nice blocky handle shape. Give it a curve on one side to make it look extra handley. You can also add some grip lines on the back if you like.
Join the handle to the body with 2 semi-circles next to each other and draw a moon shape in the corner
No ray gun is complete without a fin! Draw a couple of curved lines that join together at a point at the top of the body to make your ray gun look a bit like an awesome futuristic shark!
Finally, add in buttons and lightning bolts and wires and whatever you like to make your ray gun look proper spacey and epic!