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Ken
<br> I've been reading thru a couple of the threads dealing with what twist to go with for a couple different cartridges. Can a bullet be over stablized with to fast a twist? Thanks. dempsey

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<br>dempsey - Bullets can be over-stabilized This is generally not a problem out to 100 to 200 yards, but does become a problem at longer ranges. Tractability is the dynamic of the nose of the bullet following the flight path. An over-stabilized bullet retains its nose high orientation throughout the flight to the target. This is quickly identified by finding keyholes on your target at the range.
<br>
<br>One of the best exterior ballistics sites that I have found is located at http://www.nennstiel-ruprecht.de/bullfly/index.htm This site offers great insight into bullet dynamics and stability

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Related question- can pushing a bullet too fast down a tight twist actually strip the bullet right on past the groves and cause problems?
<br>I was advised by Sierra not to use light for caliber bullets in one of my rifles, but they didn't tell me why, just that it would be moving faster than designed for.


















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I've never seen it happen but have long heard that it can occur. The term for it, IIRC, is "stripping in the bore." As I understand it, the rifling is too shallow, the bullet too soft, etc, for the bullet to follow the rifling.
<br>
<br>Sierra's advice more likely referred to the probability that your rifle would give the lighter bullets the deadly (for the bullet) combination of both too much velocity and too much spin.
<br>
<br>I once saw about ten out of twelve 75-grain Hornady A-Max .224s become bursts of gray dust just a few yards from the muzzle -- ammo had gotten BADLY overheated in an MTM box exposed to direct sunlight too long, out on the central Wyoming plains. Rounds allowed to cool in the shade went the full distance -- one a head shot on a badger at 880 yards. (NOT one of MY shots, alas!).


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Back to the original question: "Can a bullet be overstabilized with too fast a twist?"
<br>
<br>Yes.
<br>
<br>An overly stable bullet travels its full, extreme trajectory in the same slightly tip-high angle of its exit from the slightly muzzle-high angle of the bore. IOW, the farther it goes, the more nearly sideways it meets the air it's passing through. So it slows-down faster than a barely stable bullet with the same launch velocity.
<br>
<br>Ideally stable bullets are just barely stable enough to settle into tip-forward flight without yawing or tumbling. The barely stable bullet travels its full, extreme trajectory (which is longer and "flatter" as a result) tip-forward all the way.
<br>
<br>This is one reason that matching twist length to bullet length is both crucial and (within limits) flexible.
<br>
<br>


"Good enough" isn't.

Always take your responsibilities seriously but never yourself.



















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Ken,
<br>
<br>I have always read that Winchester introduced the 32 Special in the Model 1894 with a slower twist because the 30-30 wouldn't handle reloads with black powder. I believe that the 32 Special twist is the same as the 32-40, which was primarily designed for competative shooting using BP. Is it possible that the 30-30's faster twist over-stabilized the bullets of the day which resulted in a less accurate cartridge/rifle combination? If so, Winchester's answer appears to have been the creation of a hybrid of the 30-30 case and the proven 32-40 bore, bullet, and twist. Although the 32 Special is often slandered in the gun writing press, I've never seen any problem with the couple that I've owned.
<br>
<br>What do you think?
<br>
<br>Sincerely,
<br>
<br>Bearrr264

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I have some books on cast bullets at home and the question of slipping the lands and grooves was answered mathmatically many years ago. I can't remember the mans name but he wrote for the NRA. The fellow's name was E.C. Harrison or something like that but anyway he prooved mathematically that cast lead bullets could not slip the rifleing because of being driven too fast. E. C. Hxxxx did a lot of work to answer some basic questions about cast bullets. Used what we used to call Hollerity cards only sorted them by hand to reach his conclusions etc. Interesting reading.


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Rolly,
<br> I suppose you're correct, but didn't someone once prove by the same method that a bumblebee can't fly?


















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Dempsey:
<br>
<br>There are some other interesting facts and consequences of spinning bullets.
<br>
<br>* The twist rate in most rifles is actually not suited for the full range of grain weights available.
<br>
<br>* The twist rate is only one element of determining the numbers of revolutions .
<br>
<br>* The velocity also governs the rpm's.
<br>
<br>* The twist rates for bigger bullets are slower than those of smaller bullets.
<br>
<br>* Small bullets spun too fast will shed their cladding and disintegratre due to excessive centrifugal force.
<br>
<br>* Bullet spin rate has been related to penetration depth in animals!
<br>
<br>It is beneficial to use a twist rate calculator, of which there are many on the I-net, to see what happens when bullet calibers and velocities change:
<br>
<br>Caliber 30-06 (.308" )
<br>
<br>Vel/FPM......Twist rate......RPM's
<br>2000...........15.................1600
<br>2500...........16.................1875
<br>3000...........17.................2000
<br>
<br>Caliber .22-250 ( .244 )
<br>Vel/FPM......Twist rate......RPM's
<br>2000............7.................3428
<br>2500............8.................3750
<br>3000............9.................4000
<br>3500...........10................4200
<br>
<br>Some bench rest shooters select the slowest rate that will still shoot a bullet accurately.
<br>
<br>When selecting a hunting rifle the grain weight most likely to be used most of the time should be matched to the appropriate twist rate to achieve optimum performance. Usually the Manufacturers only offer a predetermined twist rate, thus rebarreled rifles or rifles custom build will be the only available opportunity to choose the preferred rate.
<br>
<br>Bill Tibbe

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Originally Posted by William_E_Tibbe

* The twist rates for bigger bullets are slower than those of smaller bullets.


What is meant by "bigger bullets" ?

If "bigger" means heavier bullets in the same calibre, then the statement is wrong because :

- heavier bullets are longer and require more gyroscopic stabilisation
- heavier bullets are usually slower

that is 2 reasons why bigger/longer bullets need a faster barrel twist rate to be stabilised.

If "bigger" means bullets of a larger diameter, then the statement is wrong also because bullets of differing diameters but of similar sectional density will be of similar lengths and will require similar gyroscopic stabilisation. Thus, if their velocities are similar, they will require similar barrel twist rates.


Is it too ambitious or too naive to look for an honest politician? Or simply a useful one?
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Originally Posted by William_E_Tibbe
Dempsey:
<br>
<br>There are some other interesting facts and consequences of spinning bullets.
<br>
<br>* The twist rate in most rifles is actually not suited for the full range of grain weights available. True
<br>
<br>* The twist rate is only one element of determining the numbers of revolutions . True<br>
<br>* The velocity also governs the rpm's. True
<br>
<br>* The twist rates for bigger bullets are slower than those of smaller bullets. FALSE! Heavier bullets require FASTER twists to properly stabalize them i.e in 223 you need a 1/7 or 1/8 to stabilize the heavier 80gr bullets, a slower 1/12 won't work with them.<br>
<br>* Small bullets spun too fast will shed their cladding and disintegratre due to excessive centrifugal force. True - I've seen them do it.<br>
<br>* Bullet spin rate has been related to penetration depth in animals! FALSE! The rotational inertia of a bullet is a very small fraction of the total energy of a bullet and is unrelated to penetration depth.
<br>
<br>Bill Tibbe


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I am sure that a .224 50gr. SPSX Hornady bullet out of a 1:9 AR @ 3,350 fps. is spinning too fast. Of 15 fired, none made it to the 100 yard target.......but my buddies tell me that they make a pretty fireworks display at about 75 yards.

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Originally Posted by magnumb
I am sure that a .224 50gr. SPSX Hornady bullet out of a 1:9 AR @ 3,350 fps. is spinning too fast. Of 15 fired, none made it to the 100 yard target.......but my buddies tell me that they make a pretty fireworks display at about 75 yards.


That combo works well in my 1:9 rifle.


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Gentleman;
I believe the RPM given above are more than a bit conservative! wink

RPM of a Fired Bullet
by Robert Treece
Volume 9, Issue 3
http://www.sierrabullets.com/index.cfm?section=techservice&page=xring&volume=9&issue=3#7

Firearms have rifling twist in the barrel to impart stability to a projectile, keeping it pointed in the right direction without "wandering around", like a well thrown football.
RPM of a bullet is calculated from a very simple formula:
Velocity times 720 (a constant) divided by twist in the barrel.
Some examples to "chew" on: .22-250 Remington with a 1x12" twist can push 55 grain bullets to 3700 fps-figured thusly; 3700 times 720 divided by 12 equals 222,000 rpm.



You could use 40 grainers high-velocity in a AR 20" with 1x7 twist and they can reach 3600 fps-that turns over 370,000 rpm; think what a 24 or 26" barrel would do with the added velocity.
Should you care? Yes, this spin also effects how a bullet expands and should be considered when selecting a bullet for a specific usage- remember that there are usually several choices in a given diameter.

If you don't know which one should be used, call!

Sierra
Technical Support: 1-800-223-8799
Toll Free Support: 1-888-223-3006


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So, given 2 bullets of exactly the same dimensions, but one with a lead core and one with a tungsten core that weighs nearly twice as much, blah, blah, B.S. and you are all full of it.

Wayne

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Originally Posted by peepsight3006
So, given 2 bullets of exactly the same dimensions, but one with a lead core and one with a tungsten core that weighs nearly twice as much, blah, blah, B.S. and you are all full of it.

Isn't it wonderful to have omniscient beings among us?

And so humble!

Let's all be thankful. (Worshipful?)


"Good enough" isn't.

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Well, Ken, if what I said is not true, I stand corrected the minute someone explains it to me. smile

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You mean that everyone except you is demonstrably full of male-bovine feces? I didn't see anything else declarative in your post that I responded to.
Originally Posted by peepsight3006
So, given 2 bullets of exactly the same dimensions, but one with a lead core and one with a tungsten core that weighs nearly twice as much, blah, blah, B.S. and you are all full of it.



"Good enough" isn't.

Always take your responsibilities seriously but never yourself.



















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I didn't intend to imply everyone was full of it, although when I re-read the thread that's how it sounded. What I meant, was making blanket statements about longer bullets in the same caliber being heavier, and that heavier bullets, even though they are dimensionally equal to a lighter one require a tighter twist rate, just isn't so. If you try to shoot a pure copper bullet at the same twist as one made with cup and core that is the same length, it will show up in stability.

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Bullet construction has much to do with it (and length). I can throw a 45gr Barnes X from a 1-8" twist and it won't blow to pieces. I know what Wayne meant, but I'm far from obtuse.....

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