If you print with the unpolished strong and flexible, check out 3D Printing Nerd's (featuring Punished Props) videoon finishing. (Thank you to Three Red Diamonds here on Shapeways for this link.)
You may need to sand the model; I often find that I can skip this step, but it depends on the material and the way you prefer to finish. Use a sandable primer (one optimized for plastic or an automotive type) and sand between coats. You can sand between metallic paint coats as well provided you use a very high-grit sandpaper.
Another option if you want an extreme gloss without the sanding is Smooth-On's XTC-3D, a hard resin.
If you make a tutorial on finishing, please be sure to state where the model came from so that people have accurate information about pricing and contacts.
You can sell finished items only if you have my explicit permission and have discussed this with me, and providing you state clearly that the base product comes from this Shapeways shop.
There is another version of this speed loader that shows as two separate listings: the main compartment as one listing, and the rod and turning knob (the two pieces of the locking mechanism) as the second. Please check the shop for these listings (the product titles will specify). This allows you to order the main body and locking mechanism in two different colors of plastic if you want dual color and would rather not paint part or any of the model.