Years after Twitter replaced the pistol emoji with a green-and-orange water gun, X has decided to change it back to a regular handgun. An X employee announced the change in a post last week.
Emoji are universal insofar as they share common designations across platforms (U+1F52B is the water pistol), which are decided by the Unicode Consortium. But it’s up to each platform owner to decide how they’re visually represented. That’s how we got the Great Cheeseburger Emoji Debacle that was resolved in November 2017.
You’ll only see the gun if you’re looking at X on the web — as of this writing, it doesn’t appear to have updated in mobile versions of the app, though that’s apparently on its way at some point.