One of the easiest “Steampunk makes” is a gun modification, or even simpler a makeover paint job. Nerf guns are a firm favourite to work with but if it’s your first attempt then use something cheap like a water pistol. There are some great ray guns around. Have a look in discount shops for water pistols and charity shops or Thrift shops for old Nerf guns and other interesting toy guns, pirate flintlocks for instance.
This is the sort of gun I like, it's a Huntsman Boomstick. You can get them on amazon as well as other stores
Step one, remove all of the seams and the “made in china” and any other logos you don't want. Use a sharp knife blade or a files or fine abrasive paper. It’s not really necessary to dismantle the gun if it’s a simple one like a water pistol. If it's got lots of detailed areas it's probably best to disassemble it, take care especially with Nerf type guns, springs can shoot out and get lost. I take photos to make sure I can reassemble it correctly.
Next rub down the whole gun with fine steel wool. Now remove all of the dust and give the gun a coat of primer, I use acrylic primer in a spray can, when that's dry I give it a coat of matt black acrylic spray paint. Nothing expensive, look around the discount shops. Not everyone bothers with the primer.
If you haven’t got a garage or shed to paint in you’ll have to wait for a dry day and work outside. You should wear wear a face mask. See the instructions on the can for drying times; it’s usually pretty quick for acrylic paint.
Now you can start painting the details in the colours of your choice. Acrylic paints are best for this, It's best to get some quality paints, the ones from Games Workshop are good but I don't like the snap tops they use these days, they're not good and the paints dry up quite quickly if not used. This is one time when cheap paints are usually not good enough, but I have found one or two cheap craft store paints which are good for some jobs. You'll have to try them to find out but if it's your first attempt at gun painting do yourself a favour and get good paints or it may not work as well as you'd like and you will be very sad.
Paints from Games Workshop and similar places may seem expensive for such small pots but as you’ll see you’ll have enough to paint a few guns. We’re going to use the “dry brush” technique for this part, if you’re painting large areas of a big gun then use a big soft brush about an inch across. Obviously for smaller details you’ll need smaller brushes, again not expensive ones; you’ll quickly ruin your best water colour brushes.
Take the colour of choice and stir it up, cocktail sticks are handy, put a very small amount of paint on the tip of the brush bristles, what you remove from the cocktail stick is more than enough, now brush it across a sheet of newspaper, remove almost all of the paint then carefully and gently brush the part of the gun you’re working on. If you see brush marks appear then you have too much paint on the brush. You want to see barely any paint appear on the gun, keep repeating until you have the effect you like, build up the paint slowly. It’s amazing how it makes the texture of the plastic pop out even though it looked smooth before. It can really look like metal rather than plastic.
This is the finished gun.