What Does Grain Weight Mean In Ammo? And Why It’s Important

Have you ever wondered what grain weight means in ammo? Of course, or else you wouldn’t be here. Plenty of people ignore grain weight altogether, whereas some shooters consider it carefully when choosing the weight due to how it can affect the gun. 

If you need a quick answer, grain weight is the weight of the bullet itself. Not the whole cartridge, just the projectile coming out of the end. It’s also common for it to be called ‘bullet weight’, so don’t get thrown off by lingo. 

As for why grain weight in bullets is important, let’s get into it. 

 

Why Is Bullet Weight Important? 

Sometimes, the weight of the bullet can make a difference depending on how you plan on using it. Remember that we’re talking about the physical weight of the round itself. The bigger the round, the more damage it does to the other guy. 

Think of this in terms of the 5.56×45. Now you have your run-of-the-mill ball ammo, the 55-grain Ball round, which is typically used as practice ammo. Nothing major. But when you compare it to 62-grain ‘green tip’ M855 rounds, then you start to see why grain weight matters. 

‘Green tips’ are your light-armor penetrating rounds. Mind you, this all depends on the load and how well the ammo is loaded, but they are supposed to punch harder down range compared to regular 55-grain 5.56×45. 

This is due to the core on the 62-grain round that, although traveling slower, is more powerful than the 55-grain. 

Heavier bullets equal more stopping power, basically.

 

How Grain Weight Affects Accuracy

As we all know, what goes up must come down. This is why new rounds are always coming out in search of loads that match accuracy and energy over a distance. Just think of how many have been invented over the years. 

And now go look at the new 8.6 Blackout. It’s insane. 

It all starts at the barrel. And another good example we will use includes the 5.56×45 once again. 

For heavier rounds, you want a shorter twist rate. And vice versa with lighter rounds. For example, if you’re going to shoot 62-grain 5.56×45 to its best ability, then you should opt for a 1:7 through 1:9 twist rate. 

You can shoot 55-grain from 1:9, but not 1:7, due to how quickly the twist rate spins the round before exiting. 1:7 will over-stabilize the round and cause it to suffer from spin-drift quicker, meaning it will drift off in its spinning direction. 

On the other hand, 1:9 is sufficient for shooting both. 55-grain was designed to function in longer twist rates, like the 1:12. But the 1:12 will not stabilize the 62-grain bullet, leaving it to suffer from tumbling quicker. 

You will find that plenty of heavier rounds still use the same amount of powder in the casing when being loaded. That is why you see rounds with lower muzzle velocities with heavier grain weights. 

The round will function as designed as long as you have the right twist rate. 

By the way, 1:12 means one twist every 12 inches. 1:9 means one twist every 9 inches. You get what I mean? 

 

Why Would One Want A Heavier/Lighter Bullet? 

When you’re not that deep into shooting, you may wonder why anyone would want a heavier or lighter bullet. Some may see this as common sense, but we’re here to learn. I’m still learning, and I do this for a living. 

Lighter bullets don’t produce as much recoil as their heavier counterparts. This is due to less weight being pushed by the gas, which allows the round to escape the barrel more easily and fly its path. 

They are usually better over a distance, remaining more stable and covering more ground before it starts going off course. The only issue with this is the further you shoot, the less stopping power you’ll have when the round gets to where it’s going. 

Heavier rounds do this, too. But they still have the advantage of being heavier, which means more stopping power over a distance. Usually, bigger rounds have more powder in the shell casing to help push it further. 

And when you’re up close, having a heavier bullet can do you wonders. With more weight going into the target, you have added stopping power. If you take 9mm as an example, you have 115, 124, and 147-grain rounds. 

But, again, heavier bullets inflict more recoil. The lack of recoil is why many people love 9mm. Once you start shooting heavier rounds, you start to lose the lower recoil. That’s why 124-grain bullets are the sweet spot for 9mm. 

But you should always train with the same weight you use in your carry ammo. So if you carry 115-grain, then you should practice with 115-grain.

But my preferred method is 124-grain.

For hunting purposes, you want heavier bullets depending on what game you’re shooting. You wouldn’t go shooting a deer with a .22 LR, now would you? That is a great way to scare it off or kill it unethically. 

 

Conclusion

Unless you’re shooting at a distance or a living target, such as hunting, you don’t have to worry about grain weight too much. It’s not going to make or break your accuracy up close, and most weight differences produce negligible differences in outcomes. 

Still, small numbers do help. 

You should have no issues as long as you consider your twist rate and ensure you’re shooting a bullet weight that works optimally with that setup. As always, you should tinker and find what’s best for you. 

Be good and take care.