@2:33: 7,000 grams squared? I think this was a mis-speak. Kinetic Energy = ½ * mv² = ½ * (mass in grains) * (velocity)² = ((mass in grains) * (velocity)²) / 2 In the case of bullets, gravity also plays a role in reducing the bullet's velocity. This is accounted for by dividing mv² by the conventional standard value of gravitational acceleration, which is 32.17405 ft/s2. So now, KE = (mv²) / (2 * 32.17405). This formula isn't complete yet though, as this assumes that we are currently designating the units of mass with POUNDS. Bullets are not measured in pounds, they are either measured in units of grams or, more commonly, GRAINS. So to convert from what we are currently using (pounds) to the unit we want to measure (grains), we divide how many grains there are in ONE POUND, which is 7,000. So, the FINAL formula becomes: KE = (mv²) / (2 * 32.17405 * 7,000) = (mv²) / (64.3481 * 7,000) Now, if you ONLY plan on using GRAINS as the unit of mass, then you could simply this formula to: KE = (mv²) / 450,436.7
Gravity doesn’t reduce the bullet velocity if the bullet’s trajectory is horizontal. You divide by 32.2(gravitational constant) because when you convert grains to pounds you are converting it to pound force, you then need to divide by 32.2 to get pound mass to use in the kinetic energy equation
I would just like to thank you, I've been on Google trying to figure out this equation for about 35 minutes thank you I can now calculate foot pounds of energy
No problem, that’s why I did it. I am not a physicist by any means so if it’s for academic purposes it may be off by a .001 percent but for average users and reloaders it will get the job done. Thanks for watching
The equation in the hornady reloading manual states bullet weight x velocity squared / 450400 that gets me the same number on the box, 728 ftlb of engery
ya, i have read different sources for the 450xxx number, but the difference is so little that it doesnt equate to much. I didnt use the loads from the box, i used my own reloads to see power levels. I was showing the box just to show where manufacturers show it.
If you're reloading, and you use a chrono to fire five rounds. Do you take the five different readings, add the totals together and divide the totals. Then taking that number using the formula as above to get an estimated Muzzle Energy?
Caliber in terms of bullet diameter, really doesn't effect FPE, but smaller bullets at greater velocity will make more FPE, Its kind of a slippery slope to be honest. but a 180 grain bullet our of a 40 sw or a 357 mag, can potentially put out the same energy, but FPE is only part of the story, Sectional density plays a big part in terms of penetration in targets as well as potential velocity it can achieve. but 180 grain 40 and 357 mag, with same velocity, will produce the same FPE, but if you put same measure of powder in the case, it wouldn't necessarily mean they would. because a 40 may have more drag, with more surface area. Requiring more powder to reach same velocity. It all depends on the variables.
Call me dumb, but where is that 450,240 number derived from? I used 450,450 and it gets me a hair closer to what a lot of the online Kinetic Energy calculators say. I would like to be dead on since I'm making an equation. Thanks for the video.
I don' think you mentioned what "K" represents. For example, "Pi" is 3.1417, and that represents how many radius's, (1/2 the diameter), will wrap around the circle. What does "K" represent?
K is a place holder for 450,240 which itself contains the conversion from grains to pounds (7000 grains per pound) and the gravitational constant to convert weight to mass (32.16 feet per second per second). This isnt exact science, as i believe the formula is for muzzle energy in a vacuum, So variations will exist. Also mainly the formula exist so that you can jut get an idea of what a reload or a particular round creates in terms of muzzle energy to help compare to other loads which is often how they are represented in literature and commercial boxes. Probably the most accurate way would be to figure the energy in joules. But this formula helps in terms of imperial units.
Thanks for that info, but it still really did not answer my question. "3.1416, (Pi, a constant), = the circumference of a circle divided by the diameter of that circle.", so what is the actual formula that defines 450,240? I don't understand why we need to add the force of gravity as we are not measuring bullet drop, but just muzzle energy at the point of the bullet leaving the muzzle. I am sure it would be a different speed/energy if the gun were fired in a vacuum, but I don't think there would be a measurable way to see the variance of speed as a result of the air quality that is in the barrel. The normal variance of bullet speeds is probably much larger than the speed differences because of the density of the air in the barrel. The units of measurement (foot=pounds or Joules, for example) should not effect accuracy unless they use 2 different formulas, and one is more accurate than the other. But other than changing the units from Joules to foot-pounds, and what ever changes you need to do with the mass to reflect the units, (Here is a great conversions site. In this case, under "energy conversions", you will find an accurate conversion from Joules to foot-pounds.), you should be able to use the same formula,--I think. :) I found this conversion calculator to be the best on line, IMO. www.onlineconversion.com/
So in the video E is the Kinetic Energy(KE) equation KE=1/2*m*v^2, where m is mass and v is velocity. As seen from the equation, Kinetic Energy is only dependent on mass and velocity, being in or out of a vacuum only effects this equation according to how the velocity is changed. K equals 2 times the conversion of grains per pound mass(lbm) times the acceleration of gravity used to convert pounds mass(lbm) to pounds force(lbf). Plugging in the numbers to get K should look like this: K= 2(32.2ft/s^2*1lbm/1lbf)7000grain/lbm = 450,800ft*lbf/s^2 This K isn't exact because the video uses a gravitational value of 32.16 instead of 32.2. This is because gravity varies across the earth's surface due mainly to latitude and elevation. You can find your local gravity at this website: www.wolframalpha.com/widgets/view.jsp?id=e856809e0d522d3153e2e7e8ec263bf2 Hope that clears up the equation and why K can vary by a small percentage.
Im not saying its a perfect scientific method, but it gets the job done when estimating bullet energy while working up loads. I did it the way many published ballistic calculators calculate.
Muhammad you forgot to times 225217 by 2, which gives you 450434. The 2 comes from the Kinetic energy equation. KE=1/2mv^2 Although this k value is slightly off it's close enough to get the job done like Shaiwassee said. It's only off because the acceleration used in this case is 32.16.
There are probably formula's for that, but that is where air density comes into play. The more dense the air is, (like colder air being more dense than warm air, for one example), the more drag it will have on the bullet. You can measure the speed physically with a chronograph at those yards, and than with this formula, you can measure the bullet energy at each of those distances. You should be as accurate as the chronograph is. If the chronograph is accurate, you should be more precise than any formula, at least with the air quality of that particular day, (or even hour).
becausw faster objects DOUBLE to power of mass.. speed is greater than mass.. this is why bruce lee punched soo hard because he was fast and had some muscle to back it up.but some MASS is required.. the general rule of thumb is to have double the speed of your mass for greater knockdown power. too much mass and you will need more energy to hit just as hard. too little mass and you will need to hit a lot more to have an effect.
It's really close. The box I'm looking at says 416 at the muzzle and I'm getting 415.9381663113 with this formula. Good video considering alot of brands don't include it on the box👍
Ya some people comment that it’s not exact, but for a reloader, or firearm enthusiast just to see where basic energy levels are at if not know. It works good enough lol.
