Muzzle energy.....

stovepipe · Posted: Fri Apr 22, 2011 2:00 pm Post subject: Muzzle energy.....

I aint no physic's major, natch, so pardon my ignorance. But this one alwaysbugged me.
How can a projectile weighing 168gr have over 2500 lb/ft of engery at any given range in a rifle that has less than 10# of free recoil @ 12" per second. That would send the shooter flying if I'm reading them figures right, cuz as I was learned, every action has an equal and opposite reaction. Not to mention put craters in the berms and blow a deer to smithereens.

Obviously there's some kinda formula or something one uses to come to a given figure at a moment in time for said projectile but...good grief, them numbers are huge! I googled this stuff but I couldnt find anything that satifies my curiosity.

Any insight on how much energy is really being carried in these projectiles and how the heck can such a small projectile create that much energy w/o sending the shooter flying rearward 30 feet?

Pumpkinslinger · Posted: Fri Apr 22, 2011 4:06 pm Post subject: Re: Muzzle energy.....

Momentum. Momentum = mass x velocity. (Note that mass = weight / gravity) The bullet and the gun have equal momentum, not equal energy, but in opposite directions. That is your equal but opposite action.

The example you give, a 168 grain bullet with 2500 ftlbs of energy gives a muzzle velocity of about 2600 ft/sec. Using PointBlank you can calculate the velocity of an 8 pound rifle firing that load. Its 12 ft/sec, with a recoil energy of 17.9 ftlbs.

Kinetic energy = mass x velocity x velocity. Energy is the ability to do work. The work in our case is making a hole, deforming the bullet, making noise and making heat.

slimjim · Posted: Fri Apr 22, 2011 5:14 pm Post subject: Re: Muzzle energy.....

Pumpkinslinger wrote:

The work in our case is making a hole, deforming the bullet, making noise and

satisfying stovey's curiosity for projects since he is prohibited from participating in Recoil therapy.

Ominivision1 · Posted: Fri Apr 22, 2011 9:00 pm Post subject: Re: Muzzle energy.....

The secret to keep users from being knocked 30' rearward is in the stock. Heres an article by Chuck Hawks on recoil.

Recoil

As far as a bullet being able to kill a game animal, think of your car hitting a deer, now when the deer is hit, the impact of the car on the deer is spread out whereas a bullet is concentrated.

Speed of the bullet is what gives it the potential.
Ex: 150gr bullet at 3000fps = 2201mph.
energy is 2998ft lbs at the muzzle, equivalent of a cars weight striking
a concentrated area of the animal.

Gil Martin · Posted: Sat Apr 23, 2011 2:44 am Post subject: Re: Muzzle energy.....

The formula that has been around for years to calculate muzzle energy is ME=V2 X Wt. Grs / 450240. It works. A 150 grain bullet traveling at 2,900 feet per second has a muzzle energy of 2,801 ft. lbs. All the best...
Gil

gelandangan · Posted: Sat Apr 23, 2011 2:59 am Post subject: Re: Muzzle energy.....

Because..

Bushmaster · Posted: Sat Apr 23, 2011 7:39 am Post subject: Re: Muzzle energy.....

Yup...I agree with Gelandangan..."Because"

PaulS · Posted: Sat Apr 23, 2011 12:04 pm Post subject: Re: Muzzle energy.....

Energy ( Kinetic energy the energy due to motion) is a derived value (it is calculated from other real values) that has little real meaning as far as we as hunters are concerned. The amount of energy (by itself) has little bearing on what kind of damage is done on impact with a target.

A sewing needle that weighs 5 grains can have the same energy as a 165 grain 30 caliber bullet and a 10 pound lead ball. The amount of damage done to a target is determined more by the projectiles weight (or mass) than by its energy. the needle will go straight through a deer at that velocity and do little damage. the 10 pound lead ball will turn the deer into mush and the bullet will effectively kill the animal when properly placed and leave the meat in edible condition.

Pumpkinslinger · Posted: Sat Apr 23, 2011 4:27 pm Post subject: Re: Muzzle energy.....

Not trying to pick a fight but kinetic energy IS an important factor, however you have to compare apples to apples. If I take two .308" 165 grain bullets and load one in a .30-30 and the other in a .300 Win Mag, which will do the most damage? The only difference is the energy available to be used on the target.

chambered221 · Posted: Sat Apr 23, 2011 5:11 pm Post subject: Re: Muzzle energy.....

What sometimes complicates this issue is the terminology !!!

For example weight and mass, Most people think it's the same thing, it's not. It's two separately applied functions. To complicate the issue even more most of us use "weight" when we should be using "mass". The term mass is defined as the amount/quantity of an object. Weight is the gravitational force on the mass.

Another term that can be confusing is "pound". Although we use it as a measure of weight, in physics it's a unit of force not weight.

stovepipe · Posted: Sat Apr 23, 2011 5:20 pm Post subject: Re: Muzzle energy.....

Well, it's explained, and the numbers jive because of a formula and I agree with Paul, it's a derived value...but it still don't sit well in my mind.

The numbers are just too high. Regardless if they are right.
I think that formula for bullets is weird, and flawed. Makes no sense as the bullet has almost no energy and can do zero work in comparison to it's given value. If you shot something weighing 2000 pounds the bullet would penetrate or bounce off depending on density and resitance. In any case, the object it struck would not or barely budge a nano-meter, much less a foot even if it were suspended. I can't wrap my head around "2000" and "ft/pounds" used in the same sentance regarding a speeding bullet. Math says one thing, brain says another...ugh!

We need to have a contest for a different rating formula so I can deal with this better as I'm getting a headache.

Winner get's one of Vince's beers.....if I don't drink 'em all first. Razz

slimjim · Posted: Sat Apr 23, 2011 6:50 pm Post subject: Re: Muzzle energy.....

Pumpkinslinger wrote:

If I take two .308" 165 grain bullets and load one in a .30-30 and the other in a .300 Win Mag, which will do the most damage? The only difference is the energy available to be used on the target.

Pkslinger, it is true that the 300 Win Mag has more kinetic energy that the .30-30. However, it also has more momentum. Maybe this example works better if two different bullet weights are used. If a .300 Win Mag launches a 165gr bullet at a deer at 100 yards and impacts at 2945 fps. A .45-70 405gr bullet would impact at 1200 fps at the same distance giving both the same momentum upon impact. However, the .300 WMag has almost 3x the force/kinetic energy. Neither will kill the deer humanly if the POI is not in the vitals. Now let the debate begin.

slimjim · Posted: Sat Apr 23, 2011 6:56 pm Post subject: Re: Muzzle energy.....

stovepipe wrote:

the object it struck would not or barely budge a nano-meter, much less a foot even if it were suspended. I can't wrap my head around "2000" and "ft/pounds" used in the same sentence regarding a speeding bullet.

Think of the bullet as a surgical instrument not a bowling ball trying to knock the game over. With the right "surgical instrument", i.e., bullet, more kinetic energy improves the surgery potential to remove vital organs.

stovepipe · Posted: Sat Apr 23, 2011 7:02 pm Post subject: Re: Muzzle energy.....

slimjim wrote:

Think of the bullet as a surgical instrument not a bowling ball trying to knock the game over. With the right "surgical instrument", i.e., bullet, more kinetic energy improves the surgery potential to remove vital organs.

Now that's an explanation I can understand. Smile

Pumpkinslinger · Posted: Sat Apr 23, 2011 7:19 pm Post subject: Re: Muzzle energy.....

Slim, in your example, which one would do the most tissue damage?