How Much Does Grain Weight Matter When It Comes To Self Defense Ammo?

Grain Weight And Self-Defense Ammunition

The topic of self-defense ammunition raises the question of projectile grain weight and the degree to which it matters. Just as with rifle ammunition and shot size in hunting, there's a variety of beliefs and preferences out there.

Does grain weight actually matter? Does it make a difference if you're carrying 9mm 147-grain or 115-grain? 165-grain vs 180-grain .40 S&W ammo? Is it really true that they all fall to 230-grain ball .45 ACP?

The short answer is that it really depends. The slightly less short answer is that a heavier projectile has some on-paper "benefits" but that they might not add up to much in the real world.

Sound complicated yet? Buckle up, buttercup, because it's about to get that way…

Velocity Vs Momentum: Lighter vs Heavier Bullets

Okay, so the first part: what you gain and lose with lighter-for-caliber bullets compared to heavy-for-caliber bullets.

Let us also clarify that we are discussing the merits of heavier or lighter grain weights for the same caliber, such as 115 gr vs 147 gr 9mm. This is not about the merits of, say, 9mm vs .40, or .45 ACP vs 10mm. Plenty of ink has already been spilled in the caliber wars.

Essentially the idea comes down velocity vs momentum. A lighter-for-caliber projectile will travel at a faster velocity, but a heavy-for-caliber projectile will have a bit more momentum. Momentum, after all, is Mass x Velocity and therefore means more force hitting the target, when quantified by a metric other than foot-pounds.

In theory.

Momentum is a simple equation, p=mv. Since the unit of momentum is kilogram meters per second, we have to use metric units. (REEEE!) Anyhow, a 115-gr projectile has a mass of 7.45 grams (0.00745 kilograms) and 1150 feet per second (ballpark velocity for 115-gr 9mm bullets) works out to 350.52 m/s. p=(0.00745 kg)(350.52 m/s), which equals 2.6114 kg m/s. A 147-gr projectile with a velocity of 950 fps (ballpark for 147-gr 9mm) would have momentum of 2.757 kg m/s.

By contrast, a 185-gr .45 ACP bullet at 1,000 fps has 3.658 kg m/s, compared to 3.8603 kg m/s for a 230-gr projectile at 850 fps.

As you can see by these back-of-the-envelope calculations, a heavier-for-caliber projectile has slightly more momentum than a lighter-for-caliber projectile sitting over the same charge of powder.

It is also the case that heavier bullets will tend to have higher sectional density than lighter bullets of the same caliber, though it's typically a very small advantage. Sectional density - the density of a section of material - is a predictor of a projectile's ability to penetrate through resistance, meaning a heavier bullet has a slightly better propensity - on paper - for penetrating deeper into tissue. For instance, many 115-gr 9mm hollow points will have an SD around 0.13, and 147-gr hollow points will have an SD around 0.16. Hardly a game-changer.

Again, for handgun bullets. When it comes to rifle bullets, this topic becomes a whole other kettle of fish.

Other Reasons For Heavier Or Lighter Handgun Ammunition

However, there are some other reasons why a person might prefer heavier or lighter handgun ammunition. This is especially important for people who shoot a suppressed pistol, and those who prefer a larger caliber than 9mm.

Let's explain.

The point of running a can is to reduce the noise level of the report. The closer to (or further over) supersonic velocities, the more noise. Heavier bullets are slower and are often subsonic, meaning an even greater noise reduction is achieved if shooting, say, 147-grain 9mm ammunition (already subsonic) or 230-grain .45 ACP ammunition, also subsonic.

As far as calibers larger than 9mm, you can actually decrease wear and tear on your pistol and curb felt recoil a bit (though not recoil energy) by switching to a heavier grain weight.

Huh?!

So, to explain that, the faster a bullet leaves the barrel the faster the slide is sent traveling back. (Sir Isaac Newton wins again.) The more violent the cycling, the more wear and tear the pistol sustains on the contact parts of the gun, which is why most manufacturers advise limited use of +P ammunition.

Also, the portion of recoil that you feel is influenced by the force of the slide going back. That's part of what makes the muzzle rise! By shooting a heavier projectile, you'll actually feel a bit less recoil since you will have reduced slide velocity.

Therefore, you can tame the felt recoil of .40 S&W or .45 ACP by shooting the slower, heavier projectile. Granted, this only works to a degree, so don't get too ahead of yourself.

However, those practical considerations aside, what are some other considerations when it comes to projectile grain weight?

Penetration And Expansion: Terminal Ballistics Of Handgun Bullets

The two attributes people are concerned about when it comes to handgun bullets are penetration and expansion. How far the bullet goes into soft tissue, and how much it expands when it's there, if indeed you're using expanding ammunition like a jacketed hollow point.

A lighter projectile travels faster, a heavier projectile has (slightly) more momentum, meaning it's carrying more energy into the target. Remember also that hollow points have an expansion threshold; too slow and they don't open up. The slower the bullet, the less reliable expansion will be.

Now, the conventional wisdom is that a heavier bullet will dump more energy into the target, and penetrate further into soft tissue though (possibly) at the cost of expansion. A lighter bullet will hit the target at a faster velocity, thereby guaranteeing more hydraulic pressure inside the body cavity and therefore more dramatic expansion at the cost of some penetration.

If a bullet fails to expand - which happens, even with premium ammo - it still can be effective by penetrating vital structures. Other people believe that the bigger the wound channel, the more rapid the blood loss and thus incapacitation will be, and thus more reliable expansion is more desirable.

So does that mean that heavier-for-caliber bullets work better in the real world?

Well...it's actually not that simple.

Sometimes Heavier Bullets Are Better, Sometimes Lighter Bullets Are Better

So, how much does this matter in the real world?

The answer?

So long as you've selected a quality bullet, and place it where you need it to go, the difference is pretty much academic.

It really depends on the bullet in question. Not all of them are necessarily created equal. Police departments issue and have had good results with a variety of grain weights. The quality of the projectile and competent marksmanship make more difference.

Modern handgun ammunition, in the traditional calibers used for defense, tends to be roughly equally effective in the field when accurately placed. 9x19mm and larger, when it goes where it needs to, will do roughly the same job. .45 ACP doesn't result in quicker incapacitation from blood loss, and .44 Magnum will not take your head clean off.

Have a look, for instance, at Lucky Gunner Labs ammunition tests. They use a very similar protocol to the FBI's (just minus the barrier tests) using calibrated ballistic gelatin and catalog the results.

Parse the 9mm ammunition, for instance, and look at when a particular load (same projectile manufacturer, design) that has data for the various grain weights.

In some cases, lighter projectiles penetrated more deeply than heavier projectiles of the same design but expanded to the same degree, such as 124-gr and 147-gr Federal HST.

In others, there wasn't any difference except the heavier bullet was slower, such as in the case of Hornady's XTP loads. In others, such as Remington's HTP loads, penetration was the same but the heavier grain weight didn't expand or didn't expand as well.

If there are any trends both in their data and other sources over time, it's that the lighter-for-caliber (115-grain 9mm or 185-grain .45 ACP) loadings tend to exhibit poorer performance, but modern JHP projectiles have improved them. 

And so on and so forth; examples abound in their test results across different calibers.

There are other ammunition testing resources out there as well, so make sure you do your own homework and learn as much as you can for yourself. 

So what's the point?

Ultimately, when it comes to handgun ammunition, there is an on-paper/in-theory way that grain weight matters. There are also some practical reasons why it might matter. When it comes to efficacy on a hostile target? What matters there is placement, and that has nothing to do with grain weight.