Expended casing w/new S&W 640
This may be a real newbie question, and may have been addressed in other posts, but I wouldn't know how to begin looking for it. I recently bought my first handgun (Smith & Wesson Model 640). Inside the case was an expended casing sealed in a small yellow envelope with all the information about the gun on the label. I was wondering what the purpose of this casing is? I haven't opened the envelope yet, because I wasn't sure if there was some legal purpose for this, such as ballistic identification if the gun is stolen or something. Any information about the casings purpose, and how it should be stored, secured, etc... would be greatly appreciated.