Originally Posted by Infidel
Originally Posted by MickeyD
Just to be a nit picker...... smile
The divisor 450,240 was change back in the late 60's or early 70's to 450,400. Apparently a group of physicists determined the results of using the earlier number didn't quite line up with some newer or more complete observations. Or so I was told a physics professor in college..

He probably owes you a refund on at least part of your tuition. There is no one person, entity, or group who decides on the value of that constant,-- it is the combination of two other numbers, one of which is well defined and the other is pretty well defined, sorta.

Kinetic energy is 1/2 m v^2. To get it in ft-lbs, you have to divide by 7000 to convert grains to pounds, and you have to divide by the acceleration due to gravity to get from slugs to foots. Standard gravity is about 32.17405 ft/sec^2, although it actually varies from place to place.

So, 2 x 7000 x 32.17405 = 450,436.7

But, feel free to use anything close that you can remember. As noted, it doesn't change the result very much. But if you remember what the number is and why it is, then you can easily get the exact number anytime you want it.

Enjoy,

You are quite correct. The conversation with him was at his loading bench and we were discussing the various formulas for finding FPE. I mentioned that I had been using the 450240 number when he stated the more accurate formula as being 450400. He went on to explain in much greater detail on the math using, iirc, in very similar details as you mentioned and the reasoning for the change in formula which I have long since forgotten.
His final comments on the issue was to simply to round it off to 450400---it was more than close enough for the purposes at hand and that if anyone thought FPE was an accurate measure of killing/stopping power that they needed to get a hell of a lot more real world experience.

~Molɔ̀ːn Labé Skýla~