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Bullet rotation vs velocity

#8
08-09-2008, 10:08 PM
 Platinum Member Join Date: Oct 2005 Location: Michigan Posts: 2,232
Quote:
 Originally Posted by royinidaho AJ, What an underhanded thing to do. Post that link, that is. I can't believe I read that whole darn thing again
Me too! and I laughed just as hard the second time at BuffaloBob's message on page 6. That was classic.

AJ
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#9
08-09-2008, 11:03 PM
 Platinum Member Join Date: May 2008 Location: South of Canada and North of Wyoming Posts: 6,068
The physics that control spinning would be basically the same as the physics that control the velocity of a bullet.

An object in motion tends to stay in motion.

A bullet shot space would never stop or slow down unless it met with amother object. Nor would it ever stop spinning.

It takes force to put an object in motion, and it takes equal force to stop that motion. The explosion of the powder charge is the force that puts the bullet into motion, and the force that causes it to spin is the velocity of the bullet combined with the frictional force of the rifling.

The force that causes the bullet to slow down is the friction it experiences from passing through air which is also the same force that slows the spinning down. Friction from air has a lot more effect on bullet velocity than bullet spin.

If you fired a bullet straight up into the air it would still be spinning when the bullet finally stopped and started falling back to earth and still be spinning when it hit the earth. Try it with a football or baseball or whatever... toss it straight up with a spin and watch while it falls back to earth with almost the same rate of spin it had going up.

That's basically it in a nutshell.
#10
08-09-2008, 11:19 PM
 Platinum Member Join Date: Jan 2007 Location: MS Posts: 1,652
I would vote for that post as my all time favorite on this site. Now having cast my vote I must try and get the beverages off my keyboard.

Quote:
 Originally Posted by AJ Peacock Me too! and I laughed just as hard the second time at BuffaloBob's message on page 6. That was classic. AJ
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#11
08-12-2008, 10:30 AM
 Platinum Member Join Date: Feb 2005 Location: USA Posts: 2,598
Re: Bullet rotation vs velocity

Quote:
 Originally Posted by Varminator 911 jwp475: You need to read the discussion AJ posted. Because the forward speed decays much faster than the spin, as the bullet travels away from the muzzle, the bullet will spin increasingly faster than 1 revolution per 10 inches. The rpm stays nearly unchanged while the forward speed rapidly decreases. Pretty simple really, but not important. With regards to bullet testing, it is important that the necessary spin be imparted at the muzzle. Spin is a combination of twist and muzzle velocity. You need an adequate mix of both to stabilize the bullet. The bullet remains stable downrange because the rpm remain virtually unchanged as the velocity decreases.
I agree. I probable didn't word my reply well enough, bit that was what I was trying to say, the spin remains relitively consant.
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#12
08-12-2008, 06:45 PM
 Bronze Member Join Date: Nov 2007 Posts: 78
Re: Bullet rotation vs velocity

Time of flight is extremely short as well, even for extreme range. I've heard figures up to 150,000 rpm. even a t.o.f. of several seconds wouldn't be long enough to slow the spin much.
#13
08-12-2008, 07:23 PM
 Official LRH Sponsor Join Date: Mar 2007 Location: Montana Posts: 2,453
Re: Bullet rotation vs velocity

No feather ruffling is intended here.

I seems that proper spin on a bullet is necessary to accurately determine what a bullet will do at any given velocity. So from what I am gathering, the only way to do this is to fire at full velocity in order to get the proper rpm's, and set the target far enough to get the desired impact velocity?

Again, I do not want to upset anyone. I just want to know, this stuff is fascinating.

Thanks, Steve
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#14
08-12-2008, 07:43 PM
 Silver Member Join Date: Dec 2007 Location: SW Texas Posts: 330
Re: Bullet rotation vs velocity

Steve:

That how I read it. You need a fully stable bullet to be sure your test is legit.

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