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Barrel Twist Rate - What Is The Difference And Are They More Accurate?

Bullets, projectiles, cases, powder, primers, and beyond are all terms used to describe a single loaded cartridge. Cartridges are both simple and complex in their design. When a cartridge is loaded, the loader must be aware of each and every component they are using. This includes everyone from the individual hand loader to the massive manufacturer. One such consideration is bullet weight. Bullets are measured in grain, and when you purchase ammo, you’ll undoubtedly see a number followed by the abbreviation gr. For example, 115 gr or grain is a very common 9mm weight. 

When shopping for ammo, you might see 5.56 ammo listed at 55 grains and 77 grains and wonder what the difference is. Today let’s define what a grain is, and why it’s important that you understand grains, as well as why they are important.

What is a Grain 

A grain is a unit of measurement for weight. In fact, it’s a very precise unit of measurement that is rather small and well suited for weighing projectiles. Grains are so small that there are 437.5 grains in an ounce. Grain as a weight measurement has a long history that goes way back to early trade, although it took some time for it to be formalized. 

Grain is defined as the weight needed for 252.458 units to balance a cubic inch of distilled water at 30 inches of mercury pressure and 62 degrees Fahrenheit for both the air and water. That sounds confusing as it is, but luckily you won’t need mercury, water, and 62 degrees all around to determine bullet weight. 

Most projectiles have a standard set of weights that accompany the various loads we see on the market. For example, 9mm commonly comes in 115, 124, and 147 grains with some less common weights along the way. Since most common calibers have common weight components, we can identify certain weights for certain tasks and for certain weapons. 

Knights Armament SR-15 1:7 Twist Rate

Why Do We Use Grains To Measure Bullets? 

Most projectiles are small in the grand scheme of the world. Bullets just aren’t that big, and for most common weights, grain is the only one that makes sense. 115 grains sounds a lot better than .262857 of an ounce. Even immensely powerful cartridges like the .557 Nitro Express, a verified elephant gun, has a projectile that weighs 750 grains. Seven hundred fifty grains equals 1.71 ounces and some change. 

Grains just make the most sense for measuring projectiles. It provides an accurate and accepted method to measure projectiles that’s easy to read and understand. 

Why Bullet Weight is Important

Let’s go back to that store counter. You’re looking at some AR-15 ammo, and you see 55 grain and 77 grain. You might ask yourself, do 22 grains really make any kind of difference when it comes to shooting? Well, you might be surprised to learn that, yes, even 22 grains make a difference in ballistic performance. 

Depending on your barrel length and barrel rifling, the weight of your projectile can be a critical component. This is more important for rifles than handguns. In your AR situations, if your barrel is shorter with a 1:7 twist, then the 77-grain rounds are the better option. If your rifle has a carbine length barrel and 1:10 twist rate, then the 55 grain is the better choice. 

Pairing the right ammo with your weapon’s configuration is critical. Projectile weights can also affect how fast they move. When you look at a caliber and the projectiles provided for it, then heavier projectiles are often slower. Slower isn’t necessarily bad though, especially when it comes to equipping your weapon with a suppressor. 

Slower, heavier rounds are often subsonic, and they lack the sonic crack that can make your ears ring. Bullet weight makes a big difference when it comes to your weapon’s performance. If you want to make the most ballistically efficient choice for your rifle, then you have to pay attention to bullet weight. 

AR-15 556 Barrel 1:8 Twist

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