Guns are useless without bullets.
Once the shot is fired and the target is hit, then it’s a mission accomplished. However, for the estimated 12 billion discarded bullets each year—not so useful anymore.
In fact, having used shells or old bullets can do more harm than benefit. For example, if you have a habit of carrying a particular slug as a sentiment, you can get detained or possibly arrested in most public transportation.
Unless you turn it into something more than just a deadly reminder like an earphone bullet perhaps?
This would require an extreme attention to detail!
You see? We can do more than a hillbilly way of carrying stuff around. The only limit to creation is an eager mind!