The above is assuming your buddy also lives in Colorado.
If he lives in a different state then you need to go through an FFL in Colorado.
If he is a good buddy I don't know that I would worry about a bill of sale... I'd just write my own note that the you bought the gun from him on a certain date for a certain amount. This is mainly for if something happens to you and your survivors have any questions.
Last edited by blume357; May 27, 2010 at 06:12 AM.