That's not a proprietary implementation, it's a font. Unicode doesn't define how a character renders more than giving a suggestion. It's fully up to the font how it should display.
Apple displays the pistol emoji as a squirt gun. That’s wrong. It has always been wrong. It will always be wrong, because a squirt gun is not a pistol. Time doesn’t erase an error. ‘Get over it’ is the wrong response: ‘Apple, stop being wrong’ is the correct one.