Thread: Bullet choice
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Old December 8, 2019, 11:28 AM   #41
TXAZ
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Join Date: September 5, 2010
Location: McMurdo Sound Texas
Posts: 3,812
Momentum is the mass x velocity, where velocity is the speed and direction. (Mass times the acceleration due to gravity is the weight.)
Two disparate objects with the same momentum will have very different energy levels on-target, such as a 750 grain bullet vs. an 80,000 lb 18 wheeler.

In ballistic events, momentum is a valid measurement for some things, but not as important as *delivered* kinetic energy, which is 1/2 x mass times the velocity squared.

As an example of equal delivered kinetic energy:
A 750 grain .50 cal round has about 8000 ft lbs of energy at 1000 yards. So does an 80,000 lb 18 wheeler going 1.7 mph. Which is more likely to stop a deer / elk / sasquatch?

As for the momentum of the 2 objects above (and as a physics teacher ), your assignment is to do the math on the difference in momentum and kinetic energy and compare the results. (Note that the "V squared" term is what makes the difference in in the kinetic energy and momentum values.) As a very very rough guide, delivered kinetic energy (listed as kinetic energy at a particular range) is sometimes used "stopping power" value.
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