When I first got into shooting, one of the things that confused me was the “grain” number listed on ammo boxes—115 gr, 124 gr, 147 gr. I knew they were all 9mm rounds, but I didn’t understand what the numbers meant or why it mattered.

If you're just getting started or even if you've been carrying for a while, it's important to know how bullet grain affects how your gun shoots, how it feels, and how it performs—especially in a self-defense situation.

Let me break it down.

What Does "Grain" Mean?

“Grain,” or “gr,” is a unit of weight. It’s used to measure how heavy a bullet is—just the actual projectile part, not the whole cartridge.

There are 7,000 grains in a pound, so when we say a bullet is 115 grains, it means that bullet weighs 115/7000 of a pound. That comes out to about 0.26 ounces—pretty light, but when you’re dealing with high speeds and energy, that weight makes a big difference.

So when you pick up a box of 9mm ammo and it says 115 gr, 124 gr, or 147 gr, you’re looking at how heavy the bullet is, not the amount of powder or the speed of the shot (although those things are related too).

Why Bullet Weight Matters

Bullet weight affects several things:

• Recoil: Heavier bullets usually have more of a push-back feeling (more recoil).
• Velocity: Lighter bullets travel faster, heavier bullets are slower.
• Penetration & Expansion: Heavier bullets often penetrate deeper, lighter bullets may expand faster depending on the type.
• Point of Impact: Different grains can hit higher or lower on your target depending on your sights and distance.

Your gun might “prefer” a certain grain in terms of accuracy and reliability. And if you carry for self-defense, the bullet grain can affect how well the round performs under stress.

Let’s take a closer look at the three most common 9mm bullet weights: 115 gr, 124 gr, and 147 gr.

115 Grain 9mm

This is one of the most common and affordable types of 9mm ammo. If you’ve ever bought bulk ammo for practice, chances are it was 115 gr.

• Pros:
• High velocity (it’s fast)
• Low recoil (easy to control)
• Cheap and easy to find
• Cons:
• Less mass means slightly less penetration
• May not perform as well through barriers
• Can feel snappy in smaller guns

Personally, I use 115 gr ammo all the time at the range. It’s great for training and target practice, especially in compact pistols where you want something that’s easy to handle. It’s also a good choice if you're just getting used to shooting and want something with lighter recoil.

124 Grain 9mm

The 124 gr bullet is kind of the “middle ground.” It’s slightly heavier than 115 gr, so it moves a little slower, but not by much. A lot of self-defense loads and duty ammo come in 124 gr, and some military and law enforcement agencies use this weight.

• Pros:
• Balanced performance (not too light, not too heavy)
• Slightly more momentum for better penetration
• Still has manageable recoil
• Often reliable in compact and full-size pistols
• Cons:
• Slightly more recoil than 115 gr
• Might cost a little more

For me, 124 gr is a solid carry option. I’ve found that in many of my carry guns, especially striker-fired pistols, 124 gr tends to cycle very smoothly and hits close to my point of aim. It gives you a little more punch than 115 gr without going overboard.

147 Grain 9mm

Now we’re talking about the heaviest of the common 9mm bullets. At 147 grains, these bullets move slower than the other two, but they carry more momentum.

• Pros:
• Deep penetration
• Excellent for suppressed pistols (they’re usually subsonic)
• More stable at longer distances
• Often more consistent in terms of expansion in defensive loads
• Cons:
• Slower velocity
• More recoil in smaller guns
• Some guns may not cycle them as reliably
• Can feel “heavier” when shooting quickly

I like 147 gr rounds when I’m running a suppressor or testing ammo for defensive use. Some of the best hollow points come in this weight class, and they’re known for solid performance through barriers like thick denim or auto glass. But you really need to test it in your own gun—some compact pistols don’t like heavier bullets, especially with weaker springs.

Which One Should You Use?

That depends on what you're doing.

• For practice: I stick with 115 gr FMJ. It’s cheap, light, and easy on the hands.
• For carry: I lean toward 124 gr or 147 gr hollow points, depending on the gun and how it cycles.
• For suppressed shooting: 147 gr subsonic ammo is the way to go—it’s quiet and smooth.

The most important thing is to test your ammo. Just because a bullet is heavier doesn’t mean it’s better for your gun or your needs. Run a couple hundred rounds of your chosen carry load through your gun to make sure it feeds, cycles, and hits where you aim.

Also, be aware that different bullet grains can impact your point of impact. For example, my Glock 19 shoots 115 gr a little higher than 124 gr at 10 yards. It’s not a huge difference, but it matters when precision counts.

Final Thoughts

When I first started carrying, I thought 9mm was just 9mm. But over time, I realized bullet grain matters more than I expected. Lighter bullets like 115 gr are great for practice, while heavier loads like 124 gr or 147 gr offer better performance for self-defense—if your gun runs them well.

At the end of the day, it’s about finding the right balance for your setup. Your gun, your carry method, and your comfort with recoil all play a role in what grain works best for you. Try different ones, pay attention to how your gun handles them, and always train with what you carry.