Gun manufacturers create firearms in many different bullet calibers because everyone has their own preference. Some appreciate narrower barrels and smaller ammunition for pinpoint accuracy. Others favor something larger, grander, and more explosive in power. No matter which caliber you like, you can almost certainly find parts that match it on this page. We have AR-15, AR-10, and AR-9 parts sorted by caliber so it will be easy to find products from your favorite brands like Bushmaster and Creedmoor build kits.