Do longer twist rates shoot lighter bullets better?
my problem is finding the right bullet in a factory load for a 1-12" rossi .223
my buddy says a long twist need light bullets and faster twists can shoot heavier bullets.
I did use 40gr NBT and i think they did well but that was a while ago, Sportsman's Guide is sold out for now though and thats the only place i got them.

your 1:12 twist should be perfect for 55 - 60 grn. bullets and lighter.  not suprising you had a 40 gr. shoot well.  your buddy's correct.  the heavier the bullet you want to use, the faster the twist you'll need to stabalize it.  good luck to ya.  klallen

i haven't found any other 40gr ammo around. it was Ultra-Max remanufactured.
what weight do you think would shoot better? 55gr or a 60gr.
My buddy has a Mini-14 (1-9") that shoots military 5.56 62gr Green Tip well

LH, the 12 in. twist should stabalize most 65 grain and lighter bullets well. ...........Incidentally, it's not the weight but the "length" of the bullet that matters. ........Paul H

As a general rule, the greater the weight the faster the twist rate needs to be.
 
HOWEVER, it's not a weight issue - it's a length and velocity issue.
 
The reason the general rule works is that in general, heavier bullets are longer... usually.
 
However, that "general rule" is less and less true these days, especially since many manufacturers are making solid copper bullets, and tungsten-core bullets - the opposite ends of the spectrum.
 
A solid copper bullet of the same weight as a lead-core bullet of the same diameter (caliber) is longer because copper is less dense than lead. Therefore, in order to have the same weight in a specific caliber, the only place for the bullet to "go" to increase weight is longer.
 
Conversely, tungsten carbide has twice the density of lead, so a bullet in a specific caliber of lead-core construction will be longer than one with a tungsten carbide core. The most gyroscopically stabile projectile is a sphere. Spheres just don't have very appealing ballistic coefficients.
 
The actual rule is: The shorter the bullet, regardless of weight, the slower the rate of twist can be and still gyroscopically stabilize the bullet.
 
That said, the real issue, in a physics sense, is rotational velocity. Rotational velocity is imparted to the bullet with the rifling, and that velocity (speed) is a function of muzzle velocity. Here's why:
 
Imagine the bullet traveling down a 1:12 twist rate (1 rotation in 12") bore at 1 foot per second muzzle velocity. When it leaves the muzzle it will be rotating at 60 rpms - (1ft per sec * 1 rev per ft * 60 sec per min = 60 revs per min.) Now let's keep the twist rate 1:12 but increase the muzzle velocity to 100 f/s. The bullet will now be spinning at 6000 rpm. Increase the muzzle velocity to 3,000 f/s and the bullet's rotational velocity becomes 180,000 revolutions per minute. The longer the object is, the faster it must revolve in order to be gyroscopically stabile. SO...
 
As is too often the case in the shooting world, it makes more "sense" to the average Joe to have a formula that just tells him whether the bullet is "stabilized" with a certain twist rate than get into the physics of what is actually going on. However, the truth remains that you cannot actually determine the "right" twist rate for a specific length (or weight if you must) bullet without considering the velocity at which the bullet will leave the muzzle.
 
On a side note - There are those in the shooting community that insist that a bullet can be "over-stabilized". There is NO mathematical, NO physical (as in physics of motion), and NO actual data to support that opinion.
 
If you google "twist rate calculators", you will find several for free on the web. With the best of them, you enter the bullet's caliber, weight, length and muzzle velocity and it will give you all sorts of info including minimum twist rate for complete gyroscopic stabilization.
 
There's the "drink o' water from a fire hydrant" answer.
 
Paul
 
PS - Paul, it looks like we were posting at the same time. Your answer was a bit more succinct than mine. :)
 
I attached an image of the output of one of the better calculators when considering the longest 60-grain .22 I could quickly find - the Sierra HPBT. As you can see, that bullet is only marginally stabilized at a 3,000 f/s MV. "Marginally stabilized" means that if the ambient conditions change, the bullet might be more stabile or less. Just one of many good reasons to own a chronograph.
 
P

wow.
 

Quote from: Lost Hunta;70138what weight do you think would shoot better? 55gr or a 60gr.
My buddy has a Mini-14 (1-9") that shoots military 5.56 62gr Green Tip well

really, either a 55 gr. or 60 gr. bullet should do real well in your rifle. you'll just have to test various options out. that's the fun part. i'd personally start by getting some 55 gr. ballistic tips but i'm a nosler kind of reloader. i've never seen a .223 not respond well to the 55 BT's. but choose your favorite flavor bullet and give them a whirl. move on from there if you don't achieve what you're looking for.
 
i have a savage fv .223 with a 1:9 twist. it shoots everything from the 37 gr. calhoon dhp's to the 75 gr. hornady a-max's well. having a fast twist just opens up the options for ya.

I've had real good success with the Winchester 45gr JHP Varmint Bullets in the cheap 40 round value pack.  I'm not sure what the intended purpose is, and of course it was in a different rifle than yours, but I actually had a hard time besting that factory load with my handloads out of my Savage.

With a 1:12 you may have issues with the 60+ grainers...
55's will work fabulous though...

Quote from: gitano;70144As a general rule, the greater the weight the faster the twist rate needs to be.
 
HOWEVER, it's not a weight issue - it's a length and velocity issue.
 
The reason the general rule works is that in general, heavier bullets are longer... usually.
 
However, that "general rule" is less and less true these days, especially since many manufacturers are making solid copper bullets, and tungsten-core bullets - the opposite ends of the spectrum.
 
A solid copper bullet of the same weight as a lead-core bullet of the same diameter (caliber) is longer because copper is less dense than lead. Therefore, in order to have the same weight in a specific caliber, the only place for the bullet to "go" to increase weight is longer.
 
Conversely, tungsten carbide has twice the density of lead, so a bullet in a specific caliber of lead-core construction will be longer than one with a tungsten carbide core. The most gyroscopically stabile projectile is a sphere. Spheres just don't have very appealing ballistic coefficients.
 
The actual rule is: The shorter the bullet, regardless of weight, the slower the rate of twist can be and still gyroscopically stabilize the bullet.
 
That said, the real issue, in a physics sense, is rotational velocity. Rotational velocity is imparted to the bullet with the rifling, and that velocity (speed) is a function of muzzle velocity. Here's why:
 
Imagine the bullet traveling down a 1:12 twist rate (1 rotation in 12") bore at 1 foot per second muzzle velocity. When it leaves the muzzle it will be rotating at 60 rpms - (1ft per sec * 1 rev per ft * 60 sec per min = 60 revs per min.) Now let's keep the twist rate 1:12 but increase the muzzle velocity to 100 f/s. The bullet will now be spinning at 6000 rpm. Increase the muzzle velocity to 3,000 f/s and the bullet's rotational velocity becomes 180,000 revolutions per minute. The longer the object is, the faster it must revolve in order to be gyroscopically stabile. SO...
 
As is too often the case in the shooting world, it makes more "sense" to the average Joe to have a formula that just tells him whether the bullet is "stabilized" with a certain twist rate than get into the physics of what is actually going on. However, the truth remains that you cannot actually determine the "right" twist rate for a specific length (or weight if you must) bullet without considering the velocity at which the bullet will leave the muzzle.
 
On a side note - There are those in the shooting community that insist that a bullet can be "over-stabilized". There is NO mathematical, NO physical (as in physics of motion), and NO actual data to support that opinion.
 
If you google "twist rate calculators", you will find several for free on the web. With the best of them, you enter the bullet's caliber, weight, length and muzzle velocity and it will give you all sorts of info including minimum twist rate for complete gyroscopic stabilization.
 
There's the "drink o' water from a fire hydrant" answer.
 
Paul
 
PS - Paul, it looks like we were posting at the same time. Your answer was a bit more succinct than mine. :)
 
I attached an image of the output of one of the better calculators when considering the longest 60-grain .22 I could quickly find - the Sierra HPBT. As you can see, that bullet is only marginally stabilized at a 3,000 f/s MV. "Marginally stabilized" means that if the ambient conditions change, the bullet might be more stabile or less. Just one of many good reasons to own a chronograph.
 
P

Hello Paul. What about Coriolis effect and more importantly, Gyroscopic Precession in regards to crosswind? Regards, Rick.

QuoteWhat about Coriolis effect and more importantly, Gyroscopic Precession in regards to crosswind?

Well, my undadulterated, not-politically-correct answer is that I'd like to meet the yahoo that introduced the shooting community to these ideas so I could strangle him 'bout half dead. The voodoo surrounding the coriolis effect has been demonstrated about forty-'leven times. For those not familiar with these "benchrest "expert" spawned" bits of smoke and miirors, I'll explain.
 
Supposedly, the handedness of the rifling in the barrel will cause the bullet to "drift" either right or left due to a phenomenon called the "coriolis effect". As with precession (I'll address that below), there is IN FACT a caculable effect on the ballistics of projectiles due to coriolis. HOWEVER, the most significant example is a WWII German cannon that shot a projectile 120 km. Frankly, I've done the math on this cannon, and while a displacement CAN be calculated, its magnitude is insignificant when compared to other ACTUAL forces acting on the projectile. The second example is with long-range sniping. I'm sorry, that's just banana oil. Again, doing the math, the displacement OVER A DISTANCE OF A MILE is considerably less than half a caliber. Have a look here http://en.wikipedia.org/wiki/Coriolis_effect#_note-5 for a thorough explanation of the coriolis effect, and note this quote:
 

QuoteA misconception in popular culture is that the Coriolis effect determines the direction in which bathtubs or toilets drain, such that water always drains in one direction in the Northern Hemisphere, and in the other direction in the Southern Hemisphere. This urban legend has been perpetuated by several television programs, including an episode of The Simpsons and one of The X-Files. In addition, several science broadcasts and publications (including at least one college-level physics textbook) have made this incorrect statement.[

[/COLOR]
 
Even college-level physics books mis-state not only the magnitude of the effect, but even the direction!
 
Next in my corss-hairs is "precession" as it effects the ballistic path. Supposedly "over-rotation" of a bullet causes its nose to rise above the line describing the long axis of the bullet. Does precession exist? Yes. Is it important for interplanteary ballistics of missiles? Yes. Is it even measureable on a scale appropriate for earthly-bound projectiles? NO!
 
Again we can thank the bench rest "experts" for this complete load of manure. Sorry, but this kind of "expert" bullwash just infuriates me. It's sole purpose is to to make into "priests" a bunch of yahoos that NEED to impress people with how "knowledgable" - and therefore important - they are. I don't care for "priests" of any sort.
 
Anyway, back to reality.
 
Again have a look here http://en.wikipedia.org/wiki/Precession to get an idea about the scale of precession of rotating objects. To the best of my knowledge, precession has NEVER been actually demonstrated to even be measurable in earthly ballistics over ANY distance. The bench rest priests have been hard at again.
 
So what do the priests say twist rate has to do with the coriolis effect and precession? Simply put, the faster the twist the greater the effect. Which, mathematically, is true. HOWEVER, you can NOT get a bullet rotating fast enough for there to be any MEASURABLE effect of either coriolis or precession. In both the coriolis effect and precession, one can CALCULATE some number that isn't zero, therefore there is some theoretical effect. HOWEVER, if you can't measure it, 1) you can't prove it, and more importantly, 2) if you can't measure it, then it's only important to priests, charlatans and snake-oil salesmen.
 
The speed of light is a good analogy here. We KNOW that the speed of light isn't infinite, and we have in fact, MEASURED it. However, when you turn off the light in your bedroom using the lightswitch by the door, you CANNOT be in bed before the light "goes out". Can we calculate both precession and the coriolis effect numbers for bullets? Yes. Do they have ANY meaning for ballistics? About the same amount as your ability to run faster than the speed of light.
 
Rick I hope you realize that this is no rail against you. You asked about these factors with regard to the twist rate topic, and unwittingly hit one of my hot-buttons about "priests" and "experts".
 
Paul

Hello Paul.....I just asked a simple question! The reason is being as an old helicopter pilot, these forces have a dramatic effect on the main rotor of a helicopter. Simply, coriolis force can be thought of this way. Get yourself spinning in a swivel chair with your arms and legs extended....as you are spinning, quickly pull your arms and legs into your body and the chair spins faster. How this would apply to a bullet is anyones guess.

Gyroscopic precession on the other hand seems applicable. Spin a gyroscope on a flat table an tap it with a pencil. You will note that the gyroscope deflects 90 degrees in the direction of spin....not in the direction of the tap. Theoritically, a bullet in flight with a clockwise spin encounters a 90 degree crosswind from the right.... it should drift to the left as we know but it should also pitch down depending on the CG of the bullet. The rear of the bullet should tilt up which lowers the nose down. Of course, I was wondering how much tilt the effect would have on a bullet in flight......you convinced me that it is negligible.

I have crossed these effects off my worry list:biggthumpup: ...thanks and regards, Rick.

QuoteI just asked a simple question!

I know Rick... Some things just spin me right up.

Quotebeing as an old helicopter pilot

[/SIZE]
 
Well THAT explains a lot. :D
 
I used to work with a helicopter pilot, and he had a poster on his office wall that said: "Helicopters don't fly, they just beat the air into submission." Having spent a minute or two in a helicopter, I thought that comment pretty much summed up helicopter "flight". :D
 

QuoteI have crossed these effects off my worry list

Well I suppose that's "good". However, I must add that in the heat of my emotional response, I didn't address your specific point, which was precession and a cross-wind. The truth is, I don't know the answer to how a bullet responds gyroscopically to a cross-wind. Your discussion seems plausible, but the one element of it that has me doubting is the analogy of 'poking' a spinning gyroscope. 'Poking' is applying a point-force, in this case relative to the CG. A cross-wind is not a point-force. An equal force would be 'applied' by the wind to the whole cross-section of the bullet exposed to the wind. Therefore, while the bullet will be displaced laterally by a cross-wind, I have a nagging doubt that it would be effected gyroscopically.
 
One of the best 'proof' of things complex, is direct observation. I have yet to see a picture of a bullet in flight demonstrating any sort of precession, even after being perturbed in a variety of ways. Indirect evidence is second best. Indirectly, we should see keyholing of some sort, especially in targets shot at long ranges in mild to heavy cross-winds. I don't have that kind of experience, but I've NEVER heard/read of anyone reporting long-range keyholing due to gyroscopic instability EXCEPT as the projectile traverses the sound barrier in the decreasing direction.
 
The bow-wave of a super-sonic projectile moves backwards as the projectile transcends the sound barrier. The leading edge of that wave is indeed a point-force relative to the CG of the bullet, which causes the gyroscopic disruption. Nonetheless, the bullet recovers very quickly gyroscopically. Unfortunately for the target shooter, the "damage" is already done. Even though the bullet regains gyroscopic stability, the PATH of the bullet is modified.
 
The bottom line, as far as I'm concerned, is: Make the twist rate of your rifle as fast as you can. The potential negative effects of coriolis and precession are microscopic, literally, compared to the benefits gained.
 
That said, some time back, I posted an analysis of how much of the chemical energy of the powder was used to spin the bullet (rotational kinetic energy), versus how much got used to move the bullet forward (translational kinetic energy). I compared "fast" twist rates to the slowest rates able to gyroscopically stabilize the bullet. In the end, the highest "waste" of energy due to spinning a bullet "too fast" was 1.0%. Most "losses" were on the order of 0.5%. So...
 
If a benchrest shooter is spinning his bullet "too fast", and its muzle energy is 3,000 ft-lbs. Then by changing to the "just fast enough" twist rate, his muzzle energy would go up to 3,030 ft-lbs. Put in terms of muzzle velocity: If his muzzle velocity is 3107 f/s producing in this case 3,000 ft-lbs of ME, and he decrease the twist rate to "just fast enough" in order to get the 3,030 ft-lbs of ME, his MV will increase to 3122 f/s.
 
A whopping 15 f/s.
 
woo hoo.

And that's the biggest change I could make.
 
That increase is probably not outside two standard deviations of the mean of his "too fast" MV. Meaning that he can't tell whether the change in velocity was due to decreased twist rate or just the normal variability the MV of his loads.
 
Paul

Paul. On Gyroscopic P. Gusts do some strange things to bullets at 400 yards......I have had some goofy groups and don't shoot long ranges on gusty days.

In the past I have purchased barrels that were on sale and then matched the bullet to the twist. This is backward.  You should pick the bullet you want to shoot and match the twist based on that.....not barrels that are on sale. Case in point is my 6.5-06 Ackley. I wanted to shoot 140's in that rifle and it didn't like them much. So, I loaded up some 120gr Accubonds and ....bingo....instant sub MOA. Now, in the great scheme of things, I lucked out as that 120 grain bullet is perfect for the caliber as a deer rifle albiet specialized as it is. The barrel was a one in ten twist.....to shoot 140's in a perfect world, I would have purchased a 1 in eight twist barrel.....95 dollars for a new Wilson barrel was too tempting to pass on. Sometimes ignorance is bliss!:biggthumpup: Regards, Rick.

QuoteYou should pick the bullet you want to shoot and match the twist based on that

I couldn't agree more. However, getting someone to provide that barrel in the twist you want is easier 'said' than 'done'. Getting what I want instead of what's available, is precisely what motivates me to build my own rifles, and try to figure out how to make my own barrels.
 
I've been crunching some more numbers, and the .375 caliber shooting the 260-grain Accubond could handle a twist rate as low as 1:28 at a muzzle velocity as low as 2600 f/s. It's difficult to find an over-the-counter barrel in .375 with a twist rate less than 1:12.
 
I have little doubt that one of the commercial barrel makers would make a .375 barrel with just about whatever twist rate that I wanted. HOWEVER, I also have little doubt that: 1) They'd make me wait 'til Christmas of 2020 to get it; 2) I'd probably have to sell one of my children into slavery to buy it; and 3) They wouldn't actually get it right 'til I had returned the first two that had 1:12 twist rates.
 
There's a 'funny' sociological twist associated with "picking a bullet and matching the barrel to it", instead of the converse. For most of my life I have sought "multiple-use" rifles, or rifle/cartridge combinations that are supposedly highly versatile. You see this basic perspective expressed indirectly over and over with thread titles like; "If you could have only ONE gun...", and "What is the best all-around rifle for North America?" and so forth. Moving from that basic view of the world, to one of building a rifle for ONE purpose alone (or even worse, one bullet ) is a long road for most... myself included. This in spite of the fact that I own rifles that are excellent examples of versatile rifles.
 
Paul
 
Oh yeah....
 

QuoteSometimes ignorance is bliss!

How I learn things most of the time.[/SIZE]

Barrel twist is an amazing thing.

To echo Rick's 10 twist for his 6.5-06, I have a 6.5 Swede sporter with a 9 twist.

I have to "work" at finding a good handload and OAL for accuracy with 140 grain bullets.  I can achieve excellent accuracy, but the window just seems tight.  With 120 grain bullets, just about any load I try works and it chews the x-ring right out.  Today with my son home from college, we took the Swede sporter to the range to try shooting some 95 grain Hornday V-max pills.  Despite the windy conditions he was keeping them sub-MOA.  Very flat shooting too btw.

150-160 grain bullets I won't bother trying in this rifle.  Those best go in the fast twist military Swede barrels.

Nels