Let's be "ballistically correct" here.
Despite the dumbing-down foisted upon the masses by the blatantly ballistically illiterate mainstream press/TV/Hollywood/academics these days, a "bullet"...
1. Is the lead/copper PROJECTILE launched from a CARTRIDGE...
2. But it is NOT the brass casing which encases the gunpowder, primer, and the unfired bullet/projectile that constitute the entire cartridge.
It may be theoretically possible to fit a small battery and LED/bulb in an empty CASE. However, I see no practical way to fit a flashlight's components into a typical 1/4 -1 inch long pistol or rifle "bullet."
In a bookstore, I once saw an action novel's cover portraying an entire CARTRIDGE being launched from a handgun's barrel. That immediately told me the writers/editors were likely metro-sexuals born/raised in some urban mecca far from the Real World, and/or were technically illiterate ditz-brain drama majors, and/or were in sync with politics grounded in disinformation and feminized emotion. So, I passed.
Ya think a flashlight made from a "bullet" would be cool? And might such a product be subsequently deemed a "cop killer" flashlight by the always technically ill-informed/anti-gun Press?
Political Correctness aside -- gag me, dear children. I'll stick to my little Peak Matterhorn lights.