Jim Taylor
Foot Pounds
Friday, March 17, 2023, 07:27

Foot-Pounds As Related To Bullet Energy

"foot-pound" = A unit of work equal to the work or energy needed to lift a one-pound weight a distance of one foot against the force of the Earth's gravity.
From: https://www.thefreedictionary.com/foot-pound

The foot-pound force is a unit of work or energy in the engineering and gravitational systems in United States customary and imperial units of measure. It is the energy transferred upon applying a force of one pound-force through a linear displacement of one foot. The corresponding SI unit is the joule.
From: https://en.wikipedia.org/wiki/Foot-pound_(energy)

Those definitions are interesting, but, Foot-Pounds as listed for rifles and handguns is something that does not exist.

There. I said it.

If "foot-pounds" is defined a the "work or energy needed to lift a one-pound weight a distance of one foot against the force of Earth's gravity", the only conclusion possible is that it does not exist when applied to rifle and handgun projectiles.

For instance: The muzzle energy of a 150 gr. bullet fired from a .30-06 is calculated at over 3000 foot-pounds. That means the bullet fired into 3000 pounds of weight should lift it one foot. Fire a 150 gr. .30-06 into a 50 pound log hanging on rope and it won't move it sideways 1 foot let alone lift it if you fired up into it from underneath! If the muzzle energy figures were true, a 50 pound log laying on the ground should roll like a tin can when shot with 3000 foot-pounds of energy. But it won't do it because muzzle energy figures are a myth.

Newton's Third Law of Motion, speaking of objects in motion, states in part: "To every Action there is always an equal Reaction: or the mutual actions of two bodies upon each other are always equal, and directed to contrary parts." If the .30-06 could actually move a 3000 pound object, can you imagine what it would do to the person firing it?

"Muzzle Energy" figures are an easy way for ammunition companies and handloaders to compare their ammunition with other ammunition. But the figures do not translate into the real world. In hunting, animals are not taken cleanly because of muzzle energy. They are taken cleanly when the hunter has the skill to properly place his shot into the anatomy of the animal so that vital organs are damaged enough to release a rapid loss of blood, dropping the blood pressure so fast that the animal is incapacitated quickly. Sometimes to do that the bullet must break or penetrate bones, which requires the bullet retain its integrity and not come apart easily. "Foot-Pounds" of muzzle energy while useful for comparing cartridges has little value beyond that. Bullet weight ... construction and design .. velocity ... all are important. For prairie dogs a nice high velocity bullet that expands easily and rapidly is great, but it won't work on large game no matter how much muzzle energy it is rated at.

Many years ago I did a test to see how hard bullets actually hit something. I built a rig that had a 48 pound Mesquite log hung on a 6 foot long arm. It swung freely and had a tape fixed to it so we could record to the 32nd of an inch how far the log moved when struck by a bullet. All bullets expended their total energy into the log. Nothing moved the log more than a few inches. If the bullet fired actually produced several hundred foot-pounds of energy the log would have been torn from the rig! This is what the ammunition fired into the log actually did.

What we were actually measuring is called "Momentum Energy" by professionals. Momentum is the amount of "push" a moving object has. Obviously the weight of the moving object is a big factor and influences the results more than velocity. So how does this translate in the real world? Not too well a lot of the time. I have been present when someone was shot and the physical reaction to several thousand pounds of energy being dumped into the body was ... underwhelming. Those of you who hunt game such as deer or elk can testify to the same thing. There is not always a physical reaction to being hit by a bullet. Not in the sense of being hit by enough power to move a heavy weight.

For a video demonstrating this watch this guy being shot at close range with a .308 NATO round on a vest.
https://www.youtube.com/watch?v=o5f1Fo4r4_I

If the .308 actually had all those thousand pounds of muzzle energy it would make a 175 pound man go flying. As well as the shooter! Thus my initial statement that muzzle energy does not really exist.