Can someone please explain firearm ballistics?

[London]

Ballistics are a weakness of mine. I have no idea how they work. Statements which sound good at face value often have contradictory results in the real world, and this is a source of confusion for me.

For example, in the Reloading section there is currently a discussion of 135gr .40 cartridges. Now we all probably know these have "More energy" because they are lighter. And at first this sounds like a great thing, right? But then we examine the lighter bullets versus heavier ones, and find the heavier bullets outperform the ones with more energy!

.40 S&W - Wikipedia, the free encyclopedia

As you can see, 135gr bullets had far more energy than 180gr, but the 180gr had better penetration and expansion! Obviously bullet design plays a role, but it's not like we're talking WWB versus Speer Gold Dots here. These were all very high-quality bullets used. With such a huge difference in energy one would expect the slower bullets to be far outclassed by the lighter ones.

So what gives? Why is energy, which seems so to be such a vital variable, not really proving its value in the real world? Does anyone know of a good online article or book which can clarify the subject? I'm tired of getting my brain all twisted around by counter-intuitive results of bullets which on paper seem like they'd give a very different performance!

Thanks! :1zhelp:

 

[jasont]

The lighter bullets have more energy than the heavier bullets because of their velocity. Energy is equal to 1/2 x mass x velocity^2 so velocity plays a much larger role than mass in determining how much energy it has. The faster the velocity in a similar bullet is going to create a larger wound cavity which that chart does not show. It will be pushing things out of the way that much quicker as it passes through. The heavier bullet can have better expansion due to it's larger size, there is more material there to expand. Of course bullet design comes into play, but if you have two similarly designed bullets the one with more material can expand wider.

The heavier slower bullet it going to have more penetration due to the damping effect of traveling through a fluidlike structure. It will maintain it's momentum better through the gelatin than a smaller, lighter bullet. There is a larger damping force as velocity increases and less mass behind the bullet to push it through. That also means the smaller, lighter bullet is transferring it's energy to the target more quickly, hence the possibly larger wound cavity.

 

[Joseph Bell]

I don’t have an article for you but I will offer some thoughts.

If a throw a tennis ball faster than I throw a baseball at you, which one will have more energy transfer on you (more or less hurt more)? A heavier bullet has more damage at lower speed, however, a lighter bullet at faster speed will cause more internal would expansion (wound cavity). Which is better? It really depends on what you are shooting the type of environment and or possibilities of situations you may be involved in.

For my personal carry Glock 22, I use 180gr Winchester Bonded JHP’s. They have really good expansion, give me the ability to punch through car glass and the heavy hit on the threat. The Federal HST rounds are pretty good too…

 

[M. Sage]

Drag in a fluid (air and flesh included) increases exponentially with speed. It's cubed. My undedrstanding of aerodynamics is pretty basic, but there are exceptions to that rule, especially as velocity gets really high. Also, the heavier bullet, being the same diameter is effectively more dense (sectional density).The increased expansion on heavier bullets is by design. The expansion isn't as much to cause more damage than it is to bleed energy off the bullet and keep it from going down the block.

 

[Texas42]

Energy is overated. There isn't enough to matter.

 

[scap99]

I think energy numbers are a marketing ploy.
It's the whole light/fast vs heavy/slow argument.

http://ammo.ar15.com/project/Self_Defense_Ammo_FAQ/index.htm

This may hurt your brain, but had some good nuggets of info.

Sent from my DROIDX using Tapatalk

 

[London]

Energy is overated. There isn't enough to matter.

I remember reading somewhere a good punch has far more energy than a handgun round. I once saw a video of a fellow in armor being shot with a .308 at point-blank range. It wasn't even enough to push him back more than an inch or two.

Very interesting!

 

[London]

By the way, this is a little left-field, but I thought I'd say here I use 180gr rounds because they are sub-sonic. I developed a mild but anoying case of tinitus in the Air Force and am a little paranoid about making it worse (there is no cure). Forunately there is very little compromise here as the 180 seems to be a fine round anyway. (For my BUG I use +P 9MM; I'll compromise, but only so much. Better to be deaf than dead!)

 

[ZX9RCAM]

I did not realize 180gr. .40s&w was sub-sonic.......

 

[espy59lc]

I remember reading somewhere a good punch has far more energy than a handgun round. I once saw a video of a fellow in armor being shot with a .308 at point-blank range. It wasn't even enough to push him back more than an inch or two.

Very interesting!

It won't "push" the one getting shot anymore than it "pushes" the shooter...

 

[matefrio]

Yep, all slow with a huge mass or fast with a lighter mass.

I describe it this way. Dump truck traveling at 55mph hits your house, it's likely to end up in your back yard. Car hits your house going 150 mph and it'll likely explode\stop in the front room. They have about the same energy coming in but the reaction to being stopped is different.

Ok, over simplified and may not be accurate but my point being the truck continues to have energy though the house while the lighter car expends all the energy up front dramatically. Different bullets have different purposes.

 

[mikeofcontex]

As a summary... and details must be added to make numbers (unit of measure) useful, but the concepts are... KE = mass x (velocity squared) Momentum = mass x velocity

The two terms are sometimes used interchangeably, but they are not the same. IMO, penetration is much more "proportional" to momentum. Sometimes, a "power factor" is calculated using momentum x frontal area of the projectile. So, big and heavy count more with regard to the damage done to the "target." The kinetic energy values came on the scene and very fast and small projectiles suddenly looked like magic. As someone already said; marketing. Experience teaches (me) that larger diameter heavier projectiles do more damage to "targets." The best example that is most common is the 12 guage 1oz slug. It doesn't travel very fast as rifle bullets go, but it's .790 caliber and 1oz mass make it quite efffective on "targets."

 

[London]

I did not realize 180gr. .40s&w was sub-sonic.......

Yep. Less than 1,087 FPS @ sea level = no sonic boom.

 

[Younggun]

Sounds like ite would come down to something like this.

135 gr. .40 cal. bullet at 1375 fps does major damage in an 8'' deep wound track but may not reach vitals in a large or very muscular ''target''.

180 gr .40 cal. Bullet at 950 fps does moderate damage over a 14'' wound track and is almost sure to reach vitals in a large or muscular ''target''.

Is this about right? Numbers are made up so don't get me on incorrect figures.

 

[Bithabus]

By the way, this is a little left-field, but I thought I'd say here I use 180gr rounds because they are sub-sonic. I developed a mild but anoying case of tinitus in the Air Force and am a little paranoid about making it worse (there is no cure). Forunately there is very little compromise here as the 180 seems to be a fine round anyway. (For my BUG I use +P 9MM; I'll compromise, but only so much. Better to be deaf than dead!)

Most 147 gr 9mm ammo is subsonic. That's what I usually carry. Sacrifices nothing to the .40.

 

[SIG_Fiend]

The FBI produced an excellent and relatively short manual worth reading on this subject. It's still very relevant today, and cuts through a lot of the BS and sensationalism out there:

http://www.firearmstactical.com/pdf/fbi-hwfe.pdf

 

[M. Sage]

As a summary... and details must be added to make numbers (unit of measure) useful, but the concepts are... KE = mass x (velocity squared) Momentum = mass x velocity

The two terms are sometimes used interchangeably, but they are not the same. IMO, penetration is much more "proportional" to momentum. Sometimes, a "power factor" is calculated using momentum x frontal area of the projectile. So, big and heavy count more with regard to the damage done to the "target." The kinetic energy values came on the scene and very fast and small projectiles suddenly looked like magic. As someone already said; marketing. Experience teaches (me) that larger diameter heavier projectiles do more damage to "targets." The best example that is most common is the 12 guage 1oz slug. It doesn't travel very fast as rifle bullets go, but it's .790 caliber and 1oz mass make it quite efffective on "targets."

The 12 gauge slug is kind of a special case. Its huge frontal area makes up for its lack of velocity; it's one of the few rounds I know of that will get a large temporary cavity without breaking the 2000 feet/sec mark.

Sounds like ite would come down to something like this.

135 gr. .40 cal. bullet at 1375 fps does major damage in an 8'' deep wound track but may not reach vitals in a large or very muscular ''target''.

180 gr .40 cal. Bullet at 950 fps does moderate damage over a 14'' wound track and is almost sure to reach vitals in a large or muscular ''target''.

Is this about right? Numbers are made up so don't get me on incorrect figures.

Close, but not entirely accurate. Nothing in .40 cal is going to have enough velocity to do dramatic amounts of damage on the business end. You have to break about 2000 feet/second to get any benefit out of higher velocities in regard to wounding. The major advantages to a lighter handgun bullet are reduced barrier penetration and somewhat lighter recoil. With well-designed pistol bullets, you won't notice much difference in penetration during gel testing (or in people). What you will notice is how much less crap the lighter ones can go through before they get there and stay lethal.

The wound tracks for "light" and "heavy" handgun ammo are going to be close enough to call them identical.

 

[shortround]

Ballistics: Internal, External, and Terminal.

Internal ballistics take into account all the factors to achieve optimum muzzle velocity. (Inside the chamber and barrel).

External ballistics take into account all the factors that account for trajectory and probable error (accuracy) of the projectile. (Outside the barrel).

Terminal ballistics take into account all the factors that account for what the projectile does to the target upon impact.

In general, for a handgun or rifle, terminal ballistics are simply a matter of momentum not pure energy: The heavier the projectile at a given velocity, the better the penetration (with consideration that projectile designs are equal).

Hence the common confusion: A lighter projectile fired at a higher velocity may not penetrate as deeply as a heavier projectile shot at a lower velocity.

An easy way to understand this is the .45-70: It flies pretty slow, but will put down all North American game, including Bison.

Momentum is the difference between a slap and a punch to the gut.

Our ballistic research laboratories (reloading manuals) experiment with hundreds of thousands of combinations of velocity, mass, and bullet design all the time. The optimum combination depends on the desired result.

Be well.

 

[London]

Okay-

First of all, thanks for the replies. I have a better understanding of the subject, but still not a complete one. That AR15 Self-Defense Ammo article was very good. I'd glanced at it a few times before but never read it all until now. Pretty interesting that no matter what the caliber, almost all high-end bullets were capable of performing nearly identical in the gel! I'll read the FBI report this weekend.

So as far as I understand, a light bullet will start off with more energy, but also lose that energy more quickly, whereas a heavier bullet has a bit more even loss of energy. So I guess that's a pretty good explanation of why more energy wasn't all it seemed to be. It also makes sense that a lot of people use the terms "Energy" and "Momentum" interchangeably, thanks in no small part to wonder-bullet marketing.

Very interesting subject!

 

[shortround]

Energy and Momentum cannot be used interchangeably.

Also mv and foot pounds of energy deposited on the target are purely mathematical, not a total view of the destructive potential of a given projectile as it impacts the target.

Gun writers love to write about units of energy (simple math), but rarely discuss mass and momentum (higher-order mathematics and physics).

Much like the relationship/difference between horse-power and torque.

A gasoline engine tends to develop higher torque at higher RPMs, while a diesel engine tends to develop far more torque at lesser RPMs.

Enough for now before I digress.

Be well.