The modularity of the AR-15 means you can buy one rifle, and a selection of other components that can be swapped in and out of the rifle, and have a firearm capable of utilizing multiple calibers for a variety of applications. By swapping upper receivers or changing parts, you can adapt your rifle for hunting, plinking, personal defense, or long-range marksmanship. No other rifle can match the AR-15’s flexibility, which is why so many gun-owners invest heavily in their ARs.