"Puting it to sleep too early" & "Overstabalization"

[threeinadime]

Could someone explain what it means for a bullet to "go to sleep" (early) and how a bullet could be "overstabalized" and what happens if it is? Thanks

[Fiftydriver]

Dimecovers3,

Well lets see, I will give you my definition of the two terms and then others will surely give you theirs and I am sure they will all be a bit unique in some aspect.

From my understanding and testing, as a bullet is driven down a barrel of a rifle it is totally controlled by the "grip" if the rifling that has engraved into the bullet jacket.

While in the barrel, the bullet is forced to rotate around the axial center of the bore.

When the bullet is released by the muzzle, this control the rifling has over the bullet instantly stops and when it does, the now spinning bullet(results of the rifling) begins to spin around its center of gravity instead of the axial center of the rifle bore.

These two points are seldom the same. We want them to be as close as possible but this simply can not happen to perfection.

So now we have a bullet that has just left the muzzle that is trying to shed off the effects of the rifling induced spin and now it wants to rotate around its center of gravity.

Well, it takes some amount of time to do this. Picture a childs toy top. When you initially spin it there is noticable wobble in the top for the first instant it hits the groud spinning, but quickly it "Balances" if you will and spins true to its center of gravity.

This is what is referred to "going to sleep", this is the time it takes for a bullet to spin evenly and consistantly around its own center of gravity after shedding the effects of the rifling.

In conventional bullet weights, this is really not an issue as the distance it takes to "go to sleep" is relatively short, 75 to 125 yards in most cases.

With a VLD or ULD bullet, this can change to 200 yards or a bit more. With very heavy 50 BMG bullets, 250 yards is at times needed to get a totally stabilized bullet.

The longer the bullet for caliber, the longer the distance it will take for the bullet to go to sleep. Also, in most cases, the faster the twist the longer it will take, but only with long VLD or ULD bullets.

Short light bullets tend to stabilize very quickly in a fast twist barrel, well any barrel twist for that matter. Which brings us to your second topic. Many may disagree with me on this but personally, I do not feel the "Overstabilization" is an actual problem in the shooting sports.

What I do feel is a problem are bullets that are rotated to such a high rotational velocity that their jacket/core bond looses integrity and accuracy drops off or the bullet totally fails in flight.

The reason I believe this is because I have seen to many fast twist large 6mm rounds drive 55 gr Ballistic Tips into groups in the .1"s and .2"s at 100 yards. Take a 55 gr ballistic tip driven to 4500 fps in a 1-9 twist barrel and you have some severe rotational stresses on that bullet, still, in a quality built rifle, groups will be very tight with this combination.

Take the same combo but substitute a 58 gr V-Max in place of the Ballistic Tip and you will be producing small blue clouds of smoke just off the muzzle. Is this overstabilization, no, Bullet failure, or should I say, failure to use a bullet that will handle the strains of the rifle combo.

Take that same 58 gr V-Max at the same 4500 fps in a 1-13 twist barrel and you will get equal accuracy.

SO in my opinion there is no such thing as over stabilization. If the projectile retains its structural integrity, the faster you spin it the tighter it will hold the line of accuracy.

Again, just one mans opionion and I am not a BR shooter so I am sure they will offer a differing opinion and that for extreme accuracy you will get better accuracy with a slower twist on some bullets. Maybe, but I still feel this is a bullet structural issue and not a rotational or stability issue.

Good Shooting!!

Kirby Allen(50)

[Centre Punch]

Hi dimecover,
The article on long ballistics at the link below will help explain it to you
http://www.border-barrels.com/

Ian

"I meant to shoot the pike ut the duck got in the way"

[Richard338]

Over spinning (spinning faster than necessary) amplifies the effects of any mass imbalances.
This will cause a loss of accuracy. Will you notice it going from one twist number to the next? Probably not.
Benchrest guys are pretty particular about what twist they want though.

[meichele]

Technicaly you cant "over stabilize" a bullet but you CAN stabilize it or spin it faster than it needs to be. When this occurs with most factory produced bullets they tend to have less ballistic coefficient from the get go and to loose ballistic coefficient more rapidly than if they were stabilized closer to that magic stability factor of 1.5

Over spinning a bullet does however increase killing power due to the added cintrifical force created by the higher rate of spin. For most hunting combos, overspinning isnt much of a concern. The farther you wish to shoot though, the higher you need the BC. You would then want a stability factor of 1.5 vs 2.5 or 3 or more.

Hope that helps some.

[davewilson]

i've always been impressed by the small groups you guys get with these long per cal bullets at 100 yards.is this a testament to the quality of the bullets?if the center of gravity is on the center axis of the bullet,can we expect no "yaw effect" and therefor small groups at 100 yards?i've always experienced the same size groups at 200 and 100.i even shot my gun at 35,75,125 and 200 yards and got almost the same size groups at all distances.is this just a cheap bullet thing?

[meichele]

You know, sometimes there is no clear cut way to explain bullet accuracy and its relationship with stability. Science hasent yet proved why some bullet/twist/velocity combos will shoot tighter groups at 300 than 100 or better at 1000 than 600. There are a lot of theroies but not too much physical proof. As a general rule of thumb, bullet accuracy will be better at 100 than 25 yards and then from there it will get bigger by varing degrees. THIS IS ONLY FOR AVERAGE BULLETS FROM AVERAGE RIFLES!! Many times though you will find that groups might be 1 MOA at 100 and .5 - .75 MOA at 300 yards and beyond. Then there are the exceptionaly rare cases where actual measuments improve with distance. Rare it is, but it does happen where you might see a 6" group at 600 yards and a 4" group at 1K. Impossible? No its not impossible, it happens. I have yet to find someone who can accuratly explain it from a scientifec point of view. Some factors may include cheap bullets that may have a small air pocket inside the lead or jackets that arent concentric, but sometimes it just a phenomenon we dont yet understand. Thats why its important to know your rifle and load combos intimatly, so you know what its limits are.