A Guide to Understanding Bullet Grain Weight

Let’s start with some history and talk definitions before diving deep into ammo talk.

When discussing bullet weight, you’ll more than likely hear the term “grains.”

A grain is a unit of mass measurement that is only used in ballistics nowadays.

Back in antiquity, a grain would have been a set weight of, you probably guessed it, a single grain of barley. When trading, you would have X many barley grains for sale at a fixed price per grain. Because bread and wheat were so crucial to human history, the measurement of the “grain” survived with different equivalents. For modern US weights, 1 grain is equivalent to 1/7000 of a pound. You can always convert to pounds if you want by taking your bullet weight and dividing by 7000; now, how useful that is will depend on the end user.

For our talk here, forget pounds and get your brain thinking grains.

Physics & Ballistics

The next important thing to consider is a small amount of physics and the concept that “You can NOT cheat physics.” I’ll explain this in more detail later on. 

Force = Mass x Acceleration

You probably remember that from high school physics class but never had a good use for it …………………………..until now.

For a sportsman, we can more concisely write that formula as:

Damage Potential = Bullet Weight x Bullet Speed.

The faster your bullet, the more damage it will do; the heavier your bullet, the more damage it will do.

From 40,000 feet up, the answer to bullet weight seems simple: make the bullet as heavy as possible and make it go as fast as possible. This is where the “you can’t cheat physics” comes into play. It would be cool to fire a 500-grain projectile at 5000 feet per second from your pistol, but it just isn’t possible, or more correctly, it’s not practical. You would need a massive chamber to house a 500-grain projectile to start with and then a large amount of steel around the chamber and barrel to hold in the pressure, so your gun doesn’t blow up, nevermind that the recoil of something like this in your hand would surely break your wrist. To make this example work, you would need a 50 BMG that is pocketable and going 2,000 fps faster than a Barett sends it. So again, “You Can’t Cheat Physics” has some gives and takes for all bullet weights and speeds.

One last thing to remember is that all calibers have a specific pressure range that they work in. If you put too much powder and go outside that pressure range, things tend to blow up. This will come into play when we discuss why heavy bullets go slower.

Everything in the following two sections should be taken with a nice pinch of salt. There are examples outside of the norm for everything, and I will try to make it simple for newer folks to understand.

The Benefits of Heavier Bullets

Less Recoil: Objects at rest stay at rest. You’ll need a slower burning powder to move a heavier bullet without causing a massive pressure spike. You will also tend to use less powder with heavier bullets. That means the bullet will travel slower and thus cause less felt recoil to the shooter. Read that a couple of more times until you get the concept. Heavier bullets tend to cause less felt recoil making them more pleasant to shoot for some folks.

Less Noise: Because you use less powder, you produce less bang, and, if slower than the speed of sound, no crack sound, all around less noise. A .22 lr makes far less noise than a .45.

Subsonic Ability:  If you don’t have a crack sound from the sonic boom AND less bang sound, you have an excellent round for a suppressor. Most folks who shoot 9mm through a can will use 147 gr or heavier bullets because of this.

Deeper Penetration: Objects in motion stay in motion. The heavier bullet will tend to go deeper into the target than a lighter bullet because of its mass. It’s much easier to stop a Yugo than it is a freight train. A super light 45 gr 5.56 will stop shallower than a heavy 77 gr M262 at the same range.

Less Wind Resistance: Heavier bullets buck the wind a whole lot better. A heavier bullet is better in a breeze. Ballistic Coefficient also plays a significant part here, but that’s for another day.

The Benefits of Lighter Bullets

More Reliable in Semi Autos: More powder and pressure with a lighter bullet tends to make a semi-auto cycle better. A heavy subsonic .22 will not always cycle the action on a Ruger 10/22, whereas regular bulk ammo will. 

More Common: The lighter end of the “normal” ammo spectrum tends to be what most companies produce. Think 115 gr 9mm or 55 gr 5.56. That stuff is on every shelf of every sporting goods store. How often do you see 165 gr .45 or 158 gr 9mm?

More Energy: This one doesn’t always hold true, but for the most part, it is correct. A slower, heavier bullet will have less kinetic energy than a faster, lighter bullet. 

Armor Penetration: This isn’t just about two-legged threats. Wild boars have some mean shoulder bones, which a slower projectile may have an issue getting through. Faster bullets are better at penetrating armor, and lighter bullets go faster.

What Bullet Weight is Right for You?

• For plinking, get whatever is cheapest.
• If you want a little lighter recoil, go for a heavy bullet.
• Hunting will depend on the game you are talking about and the distance you are shooting. If you own a suppressor, go heavy and quiet. Also, friends don’t let friends buy hyper velocity 9mm; it’s a gimmick.
• I prefer heavy for caliber bullet loadings. They are a little softer shooting and work well with my suppressors.
• If you are new to shooting sports, get the cheapest and practice your fundamentals. Once you feel reasonably proficient, try a heavier bullet and see if you can tell the difference.

I hope I passed a little knowledge on to you guys. Leave any questions below, and I’ll do what I can to answer them.