KevinThomas said:
...I hear the same questions about whether an "overstabilized" bullet will properly nose over when it begins its descending branch, again, this coming mostly from LR shooters. I had this conversation with the late Bob McCoy some years back, and he stated that essentially, no small arms projectiles really nose over, and that all remain with their axis remaining pretty much on the same line as the line of bore at firing...
I read this passage as well and it sparked a renewed interest in a question someone asked when they saw people shooting AK's into the air in celebration.
Will those bullets fall back to earth with lethality or have no more energy as if dropped from a tall building? I didn't think so but could not back up that answer with any concrete science/physics/reason? This started me on a quest to understand what the hell was going on and let me tell you I've had to read certain explanations a million times until I understood the gobbledeegook that was being flung around. At the risk of being called a wanna be know it all, I'll try and explain what I've come to understand about it in the non-scientific terms I'm used to:
What I've learned is
these elements must be present - a rotating mass of reasonable stability (the spinning bullet), and air acting on the surface of said rotating mass. At this time, I'd like to break away into the topic of aviation and cover something called gyroscopic precession. In a prop driven airplane (for example, a P-51...my favourite 8)) the propeller out front is spinning in a beautifully balanced manner as I cruise along straight and level. If I want to nose down and
only push the stick forward, my tail will mysteriously kick out to the left and make me
yaw to the right because of the phenomena called
precession. You can see it demonstrated here:
http://footballphysics.utk.edu/balls/gyroscope.htm
That's why if Mr. Pilot wants to dive he must push the stick forward
and step on the left rudder. Now back to the spinning bullet flying through the air. The relative airflow over the bullets surface causes more drag on the right side of the bullet than on the left. This is caused because the right side of the bullet is spinning
into the air as the bullet falls
through the air and the left side of the bullet is spinning
with the relative air movement. (Like-you will swim through more water going upstream than you will downstream) This unequal amount of drag acts as a torque force that wants to
yaw the bullet to the right but because of
precession it ends up translating into a nose dip. If for arguments sake we say the momentum of the nose dip now changes the attitude of the falling bullet so much so that it starts falling through the air with the relative airflow moving across the top of the bullet, the drag forces will want to torque the bullet with opposite yaw and the nose will rise. Because these two tendancies in precession will keep each other in check, the bullet maintains it's
symmetry axis in a nice
co-ordinated parabola that leaves round holes in the 1000 yard target (or unfortunate somebody within range of those AK's
). It is still possible to have bullets hit something in a nose up attitude if it was launched at a steep enough angle and it didn't have enough elevation for precession to fully nose it down before hitting the ground but I believe that angle would have to be close to perfectly straight up. Incidentally, Retired General Hatcher has proven that a rifle bullet fired straight up will land base first because the relative airflow over the bullets surface is equal on all sides so there is no precession forces at play to cause it to deviate it's angular momentum. I hope this helps someone wade through the admittedly frustrating science behind it but it's basically what happens to a nice tight football spiral or a javelin.
