The grain of a bullet refers to the bullet’s mass / weight (projectile only, not the entire cartridge). It is a unit of measure: 437.5 Grains = 1 ounce. A bullet with a heavy grain will travel slower and lack kinetic energy, but will have more stored energy in it’s mass than a lighter bullet, when fired with the same force. The opposite it true for a light grained bullet.

What is the best grain for 9mm ammunition?

That is widely debated. It really all comes down to you and your gun. Understand that everything I say here about bullet grain is based on the various grained bullets be the same caliber and shot with the same force, ie a 93 vs 165 grain 9x19mm NATO round. That being said, let’s discuss.

When most people consider bullet grain, they are considering its affect on downrange power. Bullet weight does affect downrange power, but that is definitely not the whole story.

Since it’s typically the first consideration, let’s talk about power first. The two extreme schools of thought are “the heavier the better,” or “the faster the better.” One side feels a bullet with more mass offers more power, despite the compromise on speed. The other side feels power comes from speed, so a light bullet is better, despite the lack of mass. Both theories are right and wrong. A bullet’s energy is a combination of both mass and speed. A fast bullet is powerful, but the sacrifice of mass detracts form its power. Transversely, a heavy bullet is powerful, but the lack of speed takes from its power. Like so many things in life, balance is the name of this game. An effective round finds itself right in the middle of the curve.

Second, grain affects recoil. Think back to grade school. Newton’s First Law of Motion dictates an object at rest wants to stay at rest, which describes inertia. Newton’s Third Law of Motion says that every action has an equal and opposite reaction. Sir Isaac was also kind enough to point out that the more mass (measured in grain in this case) an object (bullet) has, the stronger it’s inertia. In other words, the more mass an object has the harder it is to change it’s state of motion. What does a dead English physicist have to do with shootin’? I’m glad you ask. Your gun is being pushed backward as forcefully and violently as the bullet is being pushed forward. Action – explosion pushes bullet forward. Reaction – bullet pushes explosion backward… Recoil! A big, heavy bullet needs more of a push to break it’s inertia and will push backwards on the gun as hard as the explosion has to push forward on the bullet. That is what recoil is, a bullet’s resistance to move and the amount of energy a bullet pushes back on the gun. Simply put, a heavier bullet will recoil harder than a lighter bullet, again, assuming both bullets are being fired with with the same force.

The third factor is accuracy. The inherent accuracy of one grain verse another depends on the specific rifling in your gun’s barrel. A barrel’s twist rate is the rate of spin and is measured in inches per rotation. A common 9mm pistol twist rate is 1:10. That means, in this case, the rifling spins the bullet one revolution every ten inches. A heavier bullet is better stabilized by a lower twist rate and a light bullet likes a higher twist rate. If you wish to fire an extremely light or heavy bullet, you should look into the best twist rate for that bullet grain and replace your barrel accordingly.

I am comfortable shooting the standard 115 Gr or 124 Gr 9mm bullet. If I feel I need more “umf” I go for +P or NATO rounds, as the higher pressure will give me the extra energy. However, mass isn’t the only factor affecting recoil. Remember, your gun is being pushed backwards as forcefully and violently as the bullet is being pushed forward. A higher pressure round, like a +p or NATO, fires its round with a more power. More power makes more recoil.

If you’re looking for the most possible downrange power, do the math. Force = mass x speed. Balance bullet mass and velocity. Shoot an suitable grain bullet from a high pressure round. If light recoil is your goal, stay away from heavy bullets, +P’s and NATO rounds. If accuracy is your game, look into your barrel’s twist rate and its best corresponding bullet grain. Try different grains to see what you and your gun shoot best.