Basic Terminal Ballistics Questions

[.455_Hunter]

Greetings,

These are questions that my office have been discussing for the past few days. Maybe you folks can answer them?

Set-up #1

Lest say you have two .38 special rounds. They are both loaded with non-deforming FMJ projectiles, lets say 158 grains and 110 grains. The nose profile of both bullets are identical, just the body is longer in the heavier projectile. Both rounds are loaded with a similar powder charge such that the muzzle energies are identical, but not the velocities. Both rounds are fired from the same test barrel into the same calibrated ballistic gelatin medium at close range.

Which one will penetrate more? The lighter, faster one; the heavier, slower one; or will they be the same? Remember, the energy levels are the same with the two loads.

Set-up #2

Identical general conditions as Set-up #1, except now the projectile momentum values are the same, not the energies.

Now which one will penetrate more? The lighter, faster one; the heavier, slower one; or will they be the same?


It is well known that if you fire a light bullet and a heavier bullet at the same velocity, the heavier bullet will penetrate more. However, the above questions are very different scenarios.

Thanks for your time and input,

Hunter

 

[Wheeler44]

You must rephrase part #2 of your questions.

except now the projectile momentum values are the same, not the energies.

Now which one will penetrate more? The lighter, faster one; the heavier, slower one; or will they be the same?

Indicates a slower heavier bullet traveling at the same speed; so which is it, slower or the same speed?

 

[.455_Hunter]

Set-Up #2 Reword-

Momentum is mass x velocity

The 158 gr. bullet is fired at 800 fps (126400 momentum units)

The 110 gr. bullet is fired at 1149 fps (126400 momentum units)

I hope this helps!

 

[RecoilRob]

Generally speaking, the momentum factor is paramount in performing penetration. So, in your first example, I'd expect the heavier bullet to penetrate farther due to its' greater momentum. (with equal energies, it must have more momentum being heavier)

Second example with equal momentum factors would also favor the heavier bullet due to its' superior sectional density. Higher SD will increase penetration with all else equal. At least this is what I'm believing at this time.....

 

[roscoe]

According to the Poncelot penetration formula, the heavier object penetrates further. Hence, the super-heavy projectiles for bear and Cape Buffalo.

 

[Big Boomer]

all else being equal, even then not, the heavier projectile will always penetrate more in the same media.

Unless you are just trying to penetrate air and shoot for distance at the same angle of incline.

Heavier projectiles will also stay on track better when encountering bone and other tough tissues.

 

[Owen Sparks]

Here is a ballistics riddle for you.
Two .45 caliber bullets both weighing 230 grains and both traveling at 850 feet per second strike a big block of gelatin test medium. The only difference is that one is a full metal jacketed and the other is a hollow point.

Which makes the bigger hole?

The hollow point you say?

No, they both make the same size hole.
How can this be? Simple, the expanding hollow point makes a much wider yet much shallower wound while the FMJ round nose makes a very deep yet narrow wound channel. They both displace the same volume of tissue. Now here is the kicker. The average human torso is only about 12 inches thick. A FMJ bullet that is capable of 24 inches of penetration zips right through leaving a small diameter hole and expends much of its energy flying downrange. An expanding hollow point that opens to .65 caliber and will only penetrate about 13 inches leaves a much larger wound track and is therefore much more effective.

 

[Big Boomer]

An expanding hollow point that opens to .65 caliber and will only penetrate about 13 inches leaves a much larger wound track and is therefore much more effective.

Depending on bullet design, and of course if you hit bone then it's kind of a coin toss. If you are considering soft tissue only, then sure, but the human body is made of all sorts of nifty stuff.

 

[LaEscopeta]

You can’t tell unless you actually test each scenario, shooting real bullets at real ballistic gelatin.

Many attempts have been made to come up with equations and model to predict penetration, but none work (except for narrow ranges of bullet size, speed, etc.) We know heavy, hard, pointed, fast and small projectiles penetrate better then light, soft, round, slow and big ones. But no one knows how much of an increase in one factor will make up for a reduction in another. This is why there is so much real testing.