Sleepy Bullets VS Sleepy Arrows(Archery)

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by 5Redman8, Feb 10, 2005.

  1. 5Redman8

    5Redman8 Well-Known Member

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    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
     
  2. Ballistic64

    Ballistic64 Well-Known Member

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    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
     
  3. getsmart

    getsmart Well-Known Member

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    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]
     
  4. 5Redman8

    5Redman8 Well-Known Member

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    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
     
  5. Ballistic64

    Ballistic64 Well-Known Member

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    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.
     
  6. 5Redman8

    5Redman8 Well-Known Member

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    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
     
  7. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    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)
     
  8. 5Redman8

    5Redman8 Well-Known Member

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    Thanks Kirby....like the "top" explanation.
     
  9. Bob S.

    Bob S. Well-Known Member

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    Kirby - I liked that explanation also. As we know as the top starts to spin down it will start to wobble more and more...due to the rotational axis not being the same as the gravitational axis? Do we see this in a bullet around the time it goes subsonic? Or are there other forces at work when we go subsonic?
     
  10. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Cowboy,

    A rifle bullets rotational velocity decreases very little over the flight of the bullet. The top slows dramatically because of friction with the surface it is spinning on.

    The air resistance to the bullet is very small so actual RPMs change slightly but very little over bullet flight. If they did slow this same amount then we would certainly be talking about a stability issue at extended range. This is why the top eventually falls over, lose of rotational velocity.

    As long as a bullet is started with enough RPMs to stabilize it it will stay that way over its flight unless it is only marginally stabilized at the muzzle but most bullets are over stabilized.

    The transition through the sound barrier is what can often cause a bullet to loose consistancy. This is because of how the sub sonic shock waves effect the bullet in flight compared to supersonic shock waves. Some bullet designs are better at this some are very poor, all are effected to some degree.

    Good Shooting!!

    Kirby Allen(50)
     
  11. Bob S.

    Bob S. Well-Known Member

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    Thanks! I thought the bullet would spin fairly constant through the whole flight time. I know that planes go through a turbulent period prior to going supersonic but have heard very little in the way of turbulence when coming back down. I suspect due to the bullets small mass any effect the shock waves have would be multiplied.
     
  12. Centre Punch

    Centre Punch Well-Known Member

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    Fiftydriver,
    Dr Geoffry Kolbe of Border barrels, Scotland published a conflicting view in the late 90s
    Source http://www.border-barrels.com/articles/art1.htm
    I dont know enough about the subject to take sides,i agree with your spinning top principle but i also agree with some of Dr Kolbe's comments. Some time ago i read an article on Kenny Jarrett's "Beanfield" rifles, in which he said "if it dont group at 100yrds it aint gonna group at all". Please read the article if you do not already know of it and come back with your thoughts,as i eagerly await your comments on what Dr Kolbe has to say.
     
  13. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    I would agree with most or what Kolbe wrote in his article. In fact there was not much in there that was not exactly what I have been saying.

    What points in his article do you feel I do not agree with?

    The only theory I may question is the precession theory but he knows more about that then I do for sure so I would never challange him on that, to be honest, this is only theory anyway.

    I do disagree with him about teh problem seating VLD bullets away from the rifling producing in barrel "yaw". THis may happen in a poorly chambered rifle built to mil specs such as the 308 match rifles he is referring to.

    In my custom chambers and throats in my extreme range rifles, there simply is no where for the bullet to get out of alignment with the axis of the bore as I generally cut my extreme range throats 0.0002" over bullet diameter. This is very tight, 0.0001" on each side of the bullet only. In fact you will get rub marks on the bullet body when you chamber a round, there simply is no where for the bullet to cant.

    What I have seen with VLD bullets seated off the rifling is that teh thin jacketed bullets get horizontal velocity built up before then start rotating. The heavy, long bullet then engages the origins of the rifling and the front of the bullet begins to rotate because of the rifling.

    The middle and rear of the heavy bullet has enough inertia to resist this rotational force very a slight period of time.

    Because the bullet has a very thin jacket, this jacket can not control this "wringing" action and the bullet is twisted. Finally, enough of the bullet has been engraved by the rifling to have total control over the bullet and everything begins to rotate.

    The problem is that this Winging out has weakened the jacket/core bond and as a result, when the bullet is released from the crown, this weakened bond is inconsistant and results in shifting and expansion which results in variations in flight.

    This is nothing different then a very cheap made bullet with inconsistant jacket thicknesses and such. The bullet will now rotate around an axis point that is off dead center of the bullet and consistancy will suffer.

    Now, if we take the same bullet, same velocity and seat teh bullet so that the bullet is touching solidly into the rifling. The bullet simply can not go forward without beginning to rotate.

    Also, the horizontal velocity is still very slow at this point and the thin jacket will handle and control the stresses of getting the entire bullet rotating much better then when the bullet has gained velocity before spinning.

    Basically, it is just easier on the bullet and thus allows the thin jacketed match bullets to survive higher velocities and fast twist barrels.

    I have tested this in several rifles, the latest was one of my V-Block rifles chambered in the hot 22-6mm AI. It was fitted with a 1-8" twist Lilja 3 groove barrel of 30" in length.

    Testing the Berger 80 gr VLD bullet over RL-22. I started with the bullet seated 0.050" off the rifling and at 3300 fps the consistancy of this bullet on target dropped off dramatically.

    At 3500 fps, the bullets were not reaching the target.

    I started the process again but seated the bullets +0.020" into the rifling, hard into them. Velocity topped out at 3600 fps with groups in the 3/4" range at 500 yards.

    I also tested this with the 75 gr A-Max and it resulted in similar results.

    With the 80 gr Sierra Mk the results were different. Seated off the rifling, the Sierra bullet still reached around 3600 fps but groups at 500 yards were in the 1 3/4" range.

    Seated hard into the land the load work up showed they topped out at nearly the same velocity but groups were in teh 1" range.

    The reason, the Sierra Mk has a significantly thicker jacket then the Berger or Hornady match bullet. This thicker jacket in my opoinion, controls the Wringing effect and does not result in a weakened jacket/core bond.

    One othe rtest was with the 55 gr Hornady V-Max and the 55 gr Ballistic Tip.

    Using Rl-22 again, I started with the V-Max bullet. At 3800 fps this bullet let loose, did not matter if it was into the rifling or not.

    The 55 gr Ballistic Tip shot into 2" roups at 500 yards from 3800 fps up to a max of 4300 fps. It also did not matter what seating depth was used either.

    The difference in the two bullets, Jacket thickness. The Hornady has a traditional thin cup jacket and the combination of the 1-8 twist and the extreme velocity was far more then this bullet would handle.

    The Ballistic tip with its heavy solid base had no problem with consistancy up to 4300 fps even at the extremely high rotational velocities in this fast twist barrel.

    That is really the only area I would not fully agree with Dr. Kolbe on. The reason is because I have tested this in many rifles and it nearly always stays true to form to some degree or another.

    Other then that we believe very much the same.

    Again, he knows vastly more then I on the subject and would not disclaim anything he says, I just have another theory to explain the same happenings.

    Good Shooting

    Kirby Allen(50)
     
  14. rost495

    rost495 Well-Known Member

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    Haven't the time to read the article yet, but I can honestly say that Jarrett, the smith that he is, is full of it on his statement. I've got a few rifles that shoot much better the further out they get. In fact I can get the same accuracy at 300 that I get at 600 where as it should have doubled by that time. And this is with record setting and winning barrels fired at 600 yards. Of course they'll shoot at 100 with the right bullet, but using the best bullet (heavy) for 600, they often dont' do anything to impress you untill you pass 200 or 300 yards.

    I suspect I'm not totally on subject here though.

    jeff