When it comes to home defense, the AR-15 platform has become one of the most popular choices for American gun owners — and for good reason. It's modular, reliable, easy to shoot accurately under stress, and can be tailored to fit your home, your skill level, and your specific needs. But "AR-15" isn't a single gun; it's a whole family of configurations, and the choices you make around barrel length and caliber will have a real impact on how the rifle performs inside your house. This guide b …