Just to be a nit picker......
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,
