Explain bullet energy to me

[ForeverPA]

Short of being shot myself, I'd like to get a feel for the bullet energy upon impact. For example, Remington in 45ACP is listed at 356 ft-lb muzzle energy. What level of physical impact is this? Is it the same as dropping a 356 lb weight on someone from a foot?

[wrangler1120]

Your analogy is pretty much correct with respect to 356 ft-lbs.

Go look for slow motion videos of different bullets traveling at different velocities and hitting ballistic gel. You will get the idea of the energies involved.

[Yellowfin]

It's more like 356 lbs being applied to one foot of distance, IIRC, like a 356 lb weight driving a nail one foot into something. On the scale of rifles, like a .30-06 hitting something with 1900-2000 ft/lbs, that explains hydrostatic shock, as it's that force being transferred to the surface then the insides of something like it had a 2000 lb. weight crushing it or pulling it apart.

[RaggedEdge]

PSI would almost be a better measurement I would think.

[knight0334]

It is a measurement of kinetic energy. Kinetic is the one most often used, but momentum matters quite a bit.

The formula for kinetic is : .5 * weight(in grains) * velocity^2 / 7000 / 32.175 = energy

I'm not sure what to say as for a comparison as to what it is like. But it is the measurement of energy for that projectile at its given velocity. All objects have energy, the faster they are going, the more energy they possess. If you take (2) bullets of the same weight, propel one at 1000fps and the other at 2000fps - the fast bullet will have 4 times the energy that the slower bullet has.

Momentum is the bullet's ability to retain energy/velocity. With momentum, weight/mass has more of an affect than velocity. But velocity is still a factor at raising momentum. A heavier bullet at lower velocities will often have more momentum than a lighter weight bullet at higher velocities. That additional momentum will often allow it to penetrate further than the lighter weight bullet, however the nose/meplat of the bullet will also factor in(energy is transferred over broader surfaces faster than narrow surfaces).

[Yellowfin]

PSI would almost be a better measurement I would think.

That would more accurately describe the effect on target, but would be harder to calculate because of the different densities and diameters of targets struck. The pressure is exerted as the bullet is inside the target, very true, but only times how long it is inside the target and by how efficient the energy is transferred to the target, either by expanded frontal area, fragmentation, or tumbling/yawing. For example, a 7mm Mag using Nosler Partition hitting an elk is going to have a lot of distance to impart its energy into because that's a nice big target, and the more you bring to the party the better. Conversely the same load hitting an antelope might actually do less damage because the body thickness is much less, so the bullet will exit sooner and might not dump as much as say a .270 or .243 with a lighter bullet designed for less penetration. Further on down would be a woodchuck, which while not comfortable being hit by anything centerfire would probably lose a leg or some shoulder meat being hit by a 100 grain .243 deer round but be blown apart by a 75 grain V-max designed to blow up and dump all the energy in just a couple of inches.

Or at least that's my understanding of the physics involved.

[Coops]

You also need to consider if the bullet travels through and through (in which case not all of it's kinetic energy is transferred) or if it stops.

So getting hit in a vest where the bullet does not penetrate, will transfer all of the energy of the bullet, but if it passes through a fleshy part of the arm, very little energy will be imparted. What it feels like deepness on where it hits.

[cephas]

Although there are many formulas out there, and they are all debatable, being old school I always liked Parker Ackley kill power scale.
Energy= bullet weight x velocity squared divided by constant 450,400.
>200 lbs. minimum 900 ft. lbs.
>600 lbs. minimum 1500 ft. lbs.
>900 lbs minimum 2100 ft. lbs
Modern bullet technology has probably altered this but the advice to bring enough gun has never gone out of style.

[libra8]

Thanks, now I have a headache.

[Aggies Coach]

Thanks, now I have a headache.

Thank God.....Its not just me....