One of the reasons that the AR is America’s sweetheart when it comes to modern sporting rifles, is because of how easily built and easily customized the weapon is. Spend some time trolling the Internet and piecing together parts for your very own AR. Very quickly, as you are perusing your options for uppers, upper parts kits and barrels, you will run into this little thing called rate of twist. What is it? What does it mean? Should you really care what rate of twist your barrel has? Why? Allow us to take a moment and answer these questions in simple and common-sense terminology. Rifle barrels are rifled. Meaning, when you (SAFELY) look down the barrel of a rifle you see a series of spirals. These spirals effect the way your bullet spins as it travels down the barrel and on its way to your target. Rate of twist is the measurement that represents how many inches it takes for the bullet to spin one full turn on its way down the barrel. Rate of twist is expressed as a ratio, like a 1:7 twist, a 1:10 twist, and so forth. When it comes to the AR platform, common rate of twist varies between 1:7 and 1:12. There are 1:9 and 1:10 twists in between. So, what does this mean when it comes to selecting your barrel? Different bullet weights perform better with different rates of twist. The heavier the bullet you want to use, the faster the rate of twist should be. This allows you to properly stabilize the bullet as it is traveling down your barrel. This is not to say shooting AR ammo that is heavier or lighter out of a barrel with a rate of twist that is not ideal for it will damage the gun or the bullet. It won’t. But to effectively get all you can out of the weapon, you want to maximize the effectiveness of your ammunition. So, should you really care what rate of twist your barrel has? It depends on the purpose of the AR you are building. If you desire to shoot long range, or need deeper penetration, you will want to use a heavier bullet. Something like a 77-grain round. This means you will get the most out of your 77-grain (or 80-grain) bullet using a barrel that has a rate of twist that is 1:7. Likewise, if you are building an AR to plink around and enjoy casually shooting, you’re probably going to be running a good deal of 55-grain ammunition through it. This is because 55-grain ammo is some of the most easily available on the shelves of sporting good stores. If this is the case then a 1:9 twist rate is going to be your best bet. Again, choosing not to tailor your rate of twist to bullet weight will not result in damage. But knowing what you want to use the rifle for, and taking the time to do your homework can ensure that you get the most bang for your buck when it comes to the AR.