First of all, just about any type of object can have sentimental value to someone, depending upon how they got it. As for the use of such an item as jewelry, chaqu'un à son goût [to each his own taste]. I would bet dollars to donuts that not only was the charm not a live round, but that even cursory inspection would make abundantly clear that it never was nor could have ever been a live round (in a live round, the bullet, casing, and primer surface are three separate pieces of metal, and the casing is hollow; in the silver-colored charms that I've seen, the entire item is a solid piece of metal or chrome-plated plastic and the casing is solid except for a hole through it. Some non-silver-colored keychains I've seen look like they may have been made from real rounds, but they have no primers and the casings are obviously rendered useless by the holes drilled through them.