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# Which Chronograph?!??

#29
05-05-2013, 12:32 PM
 Platinum Member Join Date: Jun 2010 Location: greenwood, IN Posts: 4,057
Re: Which Chronograph?!??

Quote:
 Originally Posted by Greyfox My understanding is that the bullet will loose velocity from the the time it exits the barrel. It will not accelerate. In order to have exact muzzle velocity you must add back the velocity that is lost from distance that the chronograph is placed. Some ballistic programs accommodate this. It's not much, but none the less, once accounted for there is no difference using the velocities from either chronograph as long as they are accurate readings. IMO.
I've always heard that a bullet accelerates for about 25 or 30 feet, then starts dropping off. I never bothered to prove or disprove this, but thinking about it from the physics end it should accelerate a little bit. How far I can't say. A good way to think about it is that if the bullet is still climbing (with the barrel level to the earth) then it has to still be gaining rpm's. Plus there is the resistence from the barrel's bore and rifeling with a build up of gas pressure.

gotta think about that one as you maybe right.
gary
#30
05-05-2013, 05:05 PM
 Platinum Member Join Date: Jan 2008 Location: Northeast Posts: 3,619
Re: Which Chronograph?!??

Quote:
 Originally Posted by Trickymissfit I've always heard that a bullet accelerates for about 25 or 30 feet, then starts dropping off. I never bothered to prove or disprove this, but thinking about it from the physics end it should accelerate a little bit. How far I can't say. A good way to think about it is that if the bullet is still climbing (with the barrel level to the earth) then it has to still be gaining rpm's. Plus there is the resistence from the barrel's bore and rifeling with a build up of gas pressure. gotta think about that one as you maybe right. gary
Gary, I'm not so sure now. I did some searching on the topic. Turns out, it'a controversial topic. I had read a few times in the past that when a chronograph is placed 10-20 feet from the muzzle that you needed to add back some velocity to get the true muzzle velocity since the bullet slows down from air resistance immediately. Turns out the Army claimed as a result of tests years ago that the bullet did speed up when it left the.muzzle for few inches due to gases still pushing on the bullet. Since that report there has been disputes. I would think that a muzzle break would reduce this gas effect yet there are claims that there is no effect on velocity. Anyway, it seems it's an open question unless someone chimes in with additional information. I'm not so sure that it will make a big difference anyway.
Art
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"Let us speak courteously, deal fairly, and keep ourselves armed and ready"-T. Roosevelt
#31
05-06-2013, 10:44 AM
 Platinum Member Join Date: Jun 2010 Location: greenwood, IN Posts: 4,057
Re: Which Chronograph?!??

Quote:
 Originally Posted by Greyfox Gary, I'm not so sure now. I did some searching on the topic. Turns out, it'a controversial topic. I had read a few times in the past that when a chronograph is placed 10-20 feet from the muzzle that you needed to add back some velocity to get the true muzzle velocity since the bullet slows down from air resistance immediately. Turns out the Army claimed as a result of tests years ago that the bullet did speed up when it left the.muzzle for few inches due to gases still pushing on the bullet. Since that report there has been disputes. I would think that a muzzle break would reduce this gas effect yet there are claims that there is no effect on velocity. Anyway, it seems it's an open question unless someone chimes in with additional information. I'm not so sure that it will make a big difference anyway. Art
just thinking, and have not ever given thought to prove or disprove the thought. The Earth's gravity is one of the few true constants we can work with. Everyone knows that a projectile travels in an arc. In doing so we are somewhat overcomming gravitational pull (the one constant). A major factor to this is the rotational speed speed of the mass in travel. Now it would appear to me that with the barrel (in this case) set dead parallel to the Earth's surface, the peak of the arc should be the highest rate of spin on the bullet. As it drops off (going back down) the rate of spin should be decreasing. Thus relating to loss of veocity.

Back to the Army. They use an Ohler 43 (nothing like the 35P) and another super sophisticated rig to figure the B/C of their rounds (including tank ammo and small arms). If I remember right they us more than one in tandum.

what do you think?
gary
#32
05-06-2013, 11:11 AM
 Platinum Member Join Date: Jan 2008 Location: Northeast Posts: 3,619
Re: Which Chronograph?!??

Quote:
 Originally Posted by Trickymissfit just thinking, and have not ever given thought to prove or disprove the thought. The Earth's gravity is one of the few true constants we can work with. Everyone knows that a projectile travels in an arc. In doing so we are somewhat overcomming gravitational pull (the one constant). A major factor to this is the rotational speed speed of the mass in travel. Now it would appear to me that with the barrel (in this case) set dead parallel to the Earth's surface, the peak of the arc should be the highest rate of spin on the bullet. As it drops off (going back down) the rate of spin should be decreasing. Thus relating to loss of veocity. Back to the Army. They use an Ohler 43 (nothing like the 35P) and another super sophisticated rig to figure the B/C of their rounds (including tank ammo and small arms). If I remember right they us more than one in tandum. what do you think? gary
My understand
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"Let us speak courteously, deal fairly, and keep ourselves armed and ready"-T. Roosevelt
#33
05-06-2013, 11:38 AM
 Platinum Member Join Date: Oct 2008 Location: Spokane, Wa. Posts: 1,072
Re: Which Chronograph?!??

It's always been my understanding that the only reason a bullets path has an "arch" to it is because the barrel was aimed up instead of in a horizontal line to the target and that if the barrel is held horizontal the bullet is on a steady course to the ground.
#34
05-06-2013, 12:40 PM
 Platinum Member Join Date: Jan 2008 Location: Northeast Posts: 3,619
Re: Which Chronograph?!??

Quote:
 Originally Posted by B23 It's always been my understanding that the only reason a bullets path has an "arch" to it is because the barrel was aimed up instead of in a horizontal line to the target and that if the barrel is held horizontal the bullet is on a steady course to the ground.
I don't know what happened to my last post but this post reflects my understanding as well. Gravity takes effect immediately upon the bullets exit .
__________________

"Let us speak courteously, deal fairly, and keep ourselves armed and ready"-T. Roosevelt
#35
05-06-2013, 12:56 PM
 Platinum Member Join Date: Jan 2008 Location: Northeast Posts: 3,619
Re: Which Chronograph?!??

Quote:
 Originally Posted by B23 It's always been my understanding that the only reason a bullets path has an "arch" to it is because the barrel was aimed up instead of in a horizontal line to the target and that if the barrel is held horizontal the bullet is on a steady course to the ground.
I don't know what happened to my last post but this post reflects my understanding as well. Gravity takes effect immediately upon the bullets exit .
__________________

"Let us speak courteously, deal fairly, and keep ourselves armed and ready"-T. Roosevelt

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