Please explain how a bullet can "go to sleep" and get more accurate at longer ranges?

[ahhshoot]

A good BC will compensate for a bullet that is initially less accurate at closer range. Also you may want to see what your twist rate is as your bullet could be stabilizing as rotation decreases, my .02

BC is how much the projectile is affected by external forces. If it is less accurate at 100 yards doesn't mean it will be less accurate at 1500... If the bullet accurate at 100 is moved around more by wind and slowed down more by mother nature it will be inherently less accurate at longer distances. At some point the bullet that was less accurate up close will bridge the gap and maintain more accuracy way far down range.

Bullets that are less accurate up close means they aren't as consistent via INTERNAL ballistics, but those forces end as soon as the bullet leaves the muzzle, when EXTERNAL ballistics begins to take effect and will remain in effect throughout the flight of the projectile. The longer the bullet is in flight the greater the disparity will be between the bullet with a higher BC and lower BC.

I am no expert but this explanation makes sense to me.

 

[damoncali]

In former Sandia National Labs ballsitician Harold Vaughn's book, he addresses this specifically in a section on ballistic myths:

There are several ideas floating around the bench rest community that are simply not true...

"I have a load that shoots very small groups at 200 yards, but doesn't shoot well at 100 yards." The only way I can see this happening is for the bullet to be launched with a large disturbance at the muzzle. While this can happen with magnum rifles with excessive muzzle blast pressure, it is very unlikely in the case of a 6BR or 6PPC bench gun. Most likely, this is a case of poor statistics or a change of conditions"

I think he's being generous. This ain't going to happen in real life, at least not to a level that would be observable outside of a lab.

 

[Notso]

In extreme cases, it can present itself a keyholes up close, but fine downrange as the bullet slows and stabilizes once the velocity and spin are in proportion.

"Keyholes up close but fine downrange"?? So you're telling me a bullet is coming out of the barrel tumbling enough to hit a paper target sideways but then stabilizes itself downrange? I'm really having a hard time visualizing that one. maybe our definition of "keyhole is different.

 

[damoncali]

"Keyholes up close but fine downrange"?? So you're telling me a bullet is coming out of the barrel tumbling enough to hit a paper target sideways but then stabilizes itself downrange? I'm really having a hard time visualizing that one. maybe our definition of "keyhole is different.

This is how it works (oversimplified a bit). The bullet at the muzzle is somehow disturbed, and there is a large initial yaw. This yaw will decrease as the bullet goes down range, and all the while the bullet will be swerving in a corkscrew like manner. The radius of that corkscrew will decrease as you go down range. So what you get is less yaw and less swerve the farther you go.

So groups do get smaller, right? Technically, a little, maybe. But we're talking thousandths of an inch. The effect is negligible, and makes the Coriolis effect look huge in comparison. Even the initial yaw is only a few degrees and does not produce not what most people would call a keyhole - more like a slight oval.

As an aside, Franklin Mann wrote this all up in his book 100 years ago. It's fascinating. He took cards and set them up at incremental ranges (as small as 6") and shot through them all in one go. The cyclic yaw is clearly visible and he gives a more or less accurate description of the swerve of the bullet.

 

[zenbiker]

I've been away from this thread for a while just because of so many other irons in the fire, but i ran across this video http://http://youtu.be/p32xmVXYLBk demonstrating various 3D printed shotgun rounds. Shot 5 is notable because for the brief time the round is seen in the super slo-mo camera's field of view, it exhibits both nutation and precession, although to a more extreme magnitude than I suspect a supersonic projectile in accurate but not yet stable flight would exhibit. The rest of the video also has some informative, if not useful vids of unstable projectile flight patterns. Enjoy!


Sent from my iPad using Tapatalk HD

 

[secondofangle]

Well, I ignored the possibility of this phenomenon and just developed my load at 100 yards with the 350 SMK. Finally under 1/2 MOA. If this phenomenon DOES happen, I might have a 1/4 MOA gun out at 500!

 

[Sniper Uncle]

I had a Rock River Arms 24" barreled AR15 varmint rifle with a 1/8 twist. With 69 grain Sierra match bullets, it shot much smaller groups past 300 yards than it did inside of 300 yards.

Where you using the same size targets at both ranges---if so, the POA at distance looks smaller, back to LowLight's "Aim Small, Miss Small."

 

[fdkay]

Have you ever spun a coin or wooden top?
They start with a high enough initial velocity but due to an imperfect launch, they have not yet stabilized, they then right themselves and spin about their axis until they no longer have the energy to maintain balance or motion.

No bullet has an absolutely perfect base and no rifle has an absolutely perfect crown.

It is my OPINION that they can exit at other than an optimum stability and right themselves thanks to the spin, just as the top or the coin does.

I have no proof and I'm no scientist, but my wife just finished cutting my toenails for me, so I must be doing something right.

 

[Aeon1]

It is my OPINION that they can exit at other than an optimum stability and right themselves thanks to the spin, just as the top or the coin does.

I have no proof and I'm no scientist, but my wife just finished cutting my toenails for me, so I must be doing something right.

Hmm...here's a little science to ponder: http://www.snipershide.com/shooting...stics/7885-epicyclic-motion-bullet-video.html

 

[fdkay]

Hmm...here's a little science to ponder: http://www.snipershide.com/shooting...stics/7885-epicyclic-motion-bullet-video.html

Please don't confuse me with facts.

 

[secondofangle]

Have you ever spun a coin or wooden top?
They start with a high enough initial velocity but due to an imperfect launch, they have not yet stabilized, they then right themselves and spin about their axis until they no longer have the energy to maintain balance or motion.

No bullet has an absolutely perfect base and no rifle has an absolutely perfect crown.

It is my OPINION that they can exit at other than an optimum stability and right themselves thanks to the spin, just as the top or the coin does.

I have no proof and I'm no scientist, but my wife just finished cutting my toenails for me, so I must be doing something right.

Have you ever spun a top starting in a specific spot and had it become stable at the same spot over and over?

The fact that things stabalize does NOT mean that they stabalize in the same spot over and over which is what we need if it's going to be of use to us in shooting.

 

[fdkay]

Have you ever spun a top starting in a specific spot and had it become stable at the same spot over and over?

The fact that things stabalize does NOT mean that they stabalize in the same spot over and over which is what we need if it's going to be of use to us in shooting.

But then again, a top is not being launched from the same relative position as a bullet is exiting the barrel. Spinning a top is far more random then a bullet exiting the barrel.
If the bullet is coming out of a point other than the end of the barrel, then I think your problem is significantly greater than stabilization.

 

[Aeon1]

Please don't confuse me with facts.

 

[secondofangle]

But if you COULD release it in the same place with the same speed over and over, do you visualize it taking the same path each time or winding up at the same spot after a certain time elapsed again and again? I don't.

I just think there is a good deal of potential for misappropriating general principles here.

 

[fdkay]

But if you COULD release it in the same place with the same speed over and over, do you visualize it taking the same path each time or winding up at the same spot after a certain time elapsed again and again? I don't.

I just think there is a good deal of potential for misappropriating general principles here.

Well of course, you would eventually wear a spot, due to friction, causing the top to assume the same general location.

You are interjecting things into the conversation that aren't germane to the subject that I was addressing. I wasn't particularly addressing the accuracy itself, but that the bullet will "go to sleep", which of course, does lead to accuracy (or lack thereof)

I was merely postulating that the top will wobble immediately upon launch until it rights itself. It rights itself because it has enough rotational energy and momentum at the time to do so. Of course, I may be wrong. A bullet is kicked out of the bore, it has sufficient rotational energy but it's launch is not perfect due in large part to an uneven base and imperfect crown. The rotational energy overcomes the wobble and smooths it out.

 

[fdkay]

But if you COULD release it in the same place with the same speed over and over, do you visualize it taking the same path each time or winding up at the same spot after a certain time elapsed again and again? I don't.

I just think there is a good deal of potential for misappropriating general principles here.

Well of course, you would eventually wear a spot, due to friction, causing the top to assume the same general location.

You are interjecting things into the conversation that aren't germane to the subject that I was addressing. I wasn't particularly addressing the accuracy itself, but that the bullet will "go to sleep", which of course, does lead to accuracy (or lack thereof)

I was merely postulating that the top will wobble immediately upon launch until it rights itself. It rights itself because it has enough rotational energy and momentum at the time to do so. Of course, I may be wrong. A bullet is kicked out of the bore, it has sufficient rotational energy but it's launch is not perfect due in large part to an uneven base and imperfect crown. The rotational energy overcomes the wobble and smooths it out.

 

[Petrov]

My physics teacher is a sadist and doesn't believe we get our moneys worth in education till we are pulling our hair out going insane and eating pages of homework.
We did a problem on this involving projectile motion and 3 dimensional vectors. Without having to scan 3 pages of psychobabble the bullet comes out spinning but also doing a deacreasing cork screw. Some bullets have longer "cork screws" than others.

 

[Sterling Shooter]

Since the bullet is too small and fast to be seen in flight, relate its external ballistics to a child's toy top. If you spin the top while holding it at a right angle it will continue to spin a little longer before becoming unstable than if initially held at less than a right angle. Now apply that visual to a bullet leaving the muzzle where the bullet will come to rotate on its own axis from a rotation forced upon it by the bore's axis. At the muzzle the bullet may not be as stable as it will be further down range while it is still righting itself to its own axis. The bullet does not go to sleep but it is not as stable as it will eventually be. A worn out barrel, one that is really worn, will not get even close to spinning the bullet in the arena of the bullet's axis and thus the bullet comes out tumbling end over end. On the other hand, a barrel with some throat erosion will distort a bullet from its own axis enough that a whole lot of energy is consumed by the bullet upon leaving the bore to right itself and thus it will run out of energy sooner down range and begin to fly erratically and tumble sooner than it would if launched from a fresh barrel. At any rate, for me, all I want is the bullet to get nose-on to the longest distance I will be shooting to. I always expect the bullet to perform better at a closer distance for a multitude of reasons any of which easily overcoming any initial miniscule bullet instability at the muzzle.

Oh, one more thing, there is a fireworks spinning top which comes out of a bottle and spins upward in the air. As it spins faster and faster, it makes a screeching sound which becomes more high pitched in tone as it becomes more stable. It does not really serve as visual for this topic, but I just thought how much fun these things are.

 

[1lnbrdg]

Once upon a time, I used to help train the local PD sniper teams. My brother and I would shoot against the rest of the teams in competition.

I used a slightly tricked out 1903 Springfield 30.06 deer rifle with a fixed objective scope. I could always out-shoot them for group size at 200 yds but never at 100 yds, due to the objective setting.

I think that a lot of people get the objective settings on their scopes off that give them an indication that the rifle is shooting better at further distances than closer. My $.02

 

[Toast]

Jesus. Who keeps resurrecting this turd of a thread?

 

[jolofree]

Jesus. Who keeps resurrecting this turd of a thread?

8 Years later....

 

[hlee]

8 Years later....

Cicadas…