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Sleepy Bullets VS Sleepy Arrows(Archery)

 
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Old 02-10-2005, 11:12 AM
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Sleepy Bullets VS Sleepy Arrows(Archery)

With all the discussion of sleepy bullets, I thought I would provide an archers take on this topic. Personally, I can shoot proportionately smaller groups at 50yds than at 25yds.

Here is Eastons take on the situation:

http://www.eastonarchery.com/downloads/

Click on the "Tuning guide" for the download. Then check out page the bottom of page 8 through page 10. What is shows is that an improperly tuned bow will project an arrow off the string and the arrow will rotate around an axis for some distance until it stabilizes. At that point, the arow will maintain it's flight ON the axis. To me, this explains exactly why we see the PHENOMENON(sp?) known as sleepy bullets.

Also osted this on snipershide

Kyle
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Old 02-10-2005, 11:32 AM
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Re: Sleepy Bullets VS Sleepy Arrows(Archery)

No expert on the subject,but once a bullet leaves the barrel off axis,I wouldnt think it would have much chance of stabilizing back on axis.This is probably true with a bow too.A poorly tuned bow shooting arrows tail high,low left,or right will not wont have the same point of impact as a properly tuned bow.But the poorly tuned bow can have its arrow flight compensated by sight ajustment at a specific yardage.But thats not to say the poorly tuned bow would have the correct point of impact that a properly tuned bow would at all yardages.JMO
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Old 02-10-2005, 12:12 PM
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Re: Sleepy Bullets VS Sleepy Arrows(Archery)

Arrows have fletching to stabilize flight. Bullets do not. I am not convinced on the similarity, but it is interesting to think about.

I do know that the M1 Abrams has a smooth bore cannon and that the rounds are sabot with fins that extend like fletching once the round leaves the barrel. Must be better system for ballistics than the rifled barrel at least in the 104mm round. [Correction 120mm round]
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Old 02-10-2005, 12:34 PM
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Re: Sleepy Bullets VS Sleepy Arrows(Archery)

Ballistic64,

The arrow will recover and there are some good diagrams from Easton's if you get a chance to look at it.

Now whether or not a bullet can recover.....well, I have no science for that. But lets say that "runout" causes the bullet to leave the barrel with its nose off-center......could the weight and spin of the reaer section of the bullet absorb half of the "off-centered rotation" causing the bullet to fly straighter???

Lets say the bullet exits .004" off center and during flight this is spread over all of the bullet and now we have .002" of runout on the nose and .002" of runout on the rear. Could this be the stabilization we are seeing?


Kyle
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Old 02-10-2005, 01:03 PM
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Re: Sleepy Bullets VS Sleepy Arrows(Archery)

5redman8, first,Im in no way critsizing what your saying,and yes I understand that an arrow will stabilize itself from a poorly tuned bow after a certain distance.Ive shot archery for 15+ yrs.Anyway the point I was making is that the arrow point of impact from its origin will not be the same from a tuned vs. untuned bow.If,for example your bow is not tuned properly and your grouping is better at 50yds than 25yds this could be seen by having your bow properly tuned and then shooting a target at 50 yds again.I can about guarantee you that your 50 yd sight pin will require adjustment to hit the Xring.
As far as bullets off axis,the whole concept of long range accuracy revolves around the bullet leaving the chamber as close as possibly on axis and any variation otherwise has detrimental effects the farther it goes downrange.
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Old 02-10-2005, 01:22 PM
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Re: Sleepy Bullets VS Sleepy Arrows(Archery)

Ballistic....totally understabd what you are saying. It is tuned but not perfect. Did not mean to imply I was getting BETTER groups at 50....just that it was not a proportionate relationship....ie....3 inch group at 25 doesn not equate to 6inches at 50yds.

Did not think you were arguing...and i understand there are many different views on this.

Kyle
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Old 02-10-2005, 02:29 PM
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Re: Sleepy Bullets VS Sleepy Arrows(Archery)

A good example of this is proven with a childs toy TOP. When teh top is initially spun and dropped or placed in a hard surface, there is a wobble. What this wobble is, is the effects imparted on the top by the process used to accelerate its rotational velocity.

You will also notice that after just a second or so, the tops rotaion smooths up and spins almost like it is not rotating at all.

This is because the tops own inertia has taken over and faught off the effects of the intital spin acceleration. The top finds its gavitational center and rotates around that point very uniformly as long as the top is shaped correctly.

This is the same concept as what we see in bullets. The rifling is like the initial force that starts the top spinning at high rotaional speeds. The rifle does the same with the bullet.

When the top is free of this external force, it finds its center of gravity and rotates smoothly and evenly around this center of gravity.

The bullet, does the exact same thing. The center of gravity of the bullet will be different then the axial center of the bore. While the bullet is in the bore it has to rotate around the axial center of the bore simply because there is no where to go.

When the bullet is released by the muzzle, it initially wobbles just like the top does for a very short period of time. This is until the bullet finds its center of gravity and then will rotate cleanly around this point.

This is not a stability issue, it an issue concerned with a rotating projectile fighting off the forces that make the bullet rotate around the axial center of the bore and when released, it rotates around its own center of gravity.

In theory, out bullets and bore should have the same center of gravity, in reality, this is not the case and that is why it takes some distance for the bullet to "go to sleep".

Do not confuse this with a stability issue because it is not unless the bullet is not rotated fast enough. This is simply teh results of the rifling imposed onto the bullet and then the bullet shedding those forces and flying and rotating true to its center of gravity.

Good Shooting!!

Kirby Allen(50)
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