# Rifle Twist



## rgriffi (Nov 29, 2007)

How does rifle twist effect what grain bullet i can shoot out of my gun. say a rem 700 223 with a 1 in 12 twist. whats the biggest bullet i can shoot accurately.


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## People (Jan 17, 2005)

http://www.riflebarrels.com/products/ca ... _rates.htm

This states 60gr but your gun will let you know.


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## iwantabuggy (Feb 15, 2005)

They are all different. Yours may stabilize all bullets just fine, or it may like only the lightest/shortest bullets. The only way to know 100% for sure is to experiment.


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## SDHandgunner (Jun 22, 2004)

Bullet weight is not the only consideration. The actual length of the bullet itself is more important in regards to rifling twist rates than the bullets weight. A 55gr. Nosler Ballistic Tip is much longer than a 55gr. Winchester Pointed Soft Point, but both weigh the same.

Larry


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## Csquared (Sep 5, 2006)

Larry is correct. The longer the bullet, relative to it's diameter, the faster it has to spin to remain stable. The smaller the twist number the faster the bullet will spin. And one thing I think some people forget is that a faster twist is not the ONLY way to increase bullet rotation. Increasing velocity also increases spin because the harder the bullet is pushed through the rifling the faster it will spin. You proved that as a child while playing with tops.


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## Turbine Doctor (Dec 15, 2007)

Csqured is correct with pushing the bullet faster to get it to spin faster but it wont stablize any better. It is still spinning the same Rev's per foot as if it is going slower. In order to speed up the Rev's per foot you must increase the rate of twist.


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## Csquared (Sep 5, 2006)

Are you sure Doc? I had never given any thought to a bullet's stability, or lack thereof being relative to time and distance. I thought that once a bullet reached the proper rotation rate it would remain stable until it dropped cosiderably below that rate, regardless of how fast it was moving parallel with it's axis. Brings up an interesting thought. Both the rotational speed and rate of travel will obviously slow, but not at the same rate...right? So what does that mean to the bullet?


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## johngfoster (Oct 21, 2007)

You are both right. The twist rate is the number of rotations per distance traveled. This won't change by increasing the muzzel velocity. However, what stabilizes the bullet is the rotational "speed". This is a function of time, not distance, IOW, RPM vs RPF (revolutions per foot). Thus pushing a heavier/longer bullet faster out of the muzzel will increase the spin speed (not rate) which should stabilize it more.


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## Turbine Doctor (Dec 15, 2007)

John I agree with everything you said until the last sentence. I dont have all the test equipment to prove it and I may be wrong "Did I just say that" but I dont think it will stablize as much with an increase in velocity as it will with an increase in twist rate. While not trying to change the subject or muddy the waters, one has to remember the barrel harmonics when changing the velocity on there pet loads. It would be hard to prove if you are stablizing more or just getting into your barrels harmonic sweet spot. Although the bullet may stabilize more, you run the risk of getting outside of your barrels sweet spot if you have found it.

I haven't shot that many rounds through a heavy barrel but I can say that with my sporter weight barrel that a .5gr change in powder can either open or close a group for me. I did shoot a friends target weight barrel and found it would tolerate a larger velocity change then mine.


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## Csquared (Sep 5, 2006)

Thanks guys. Where have you been all my life John? I have only a basic grasp of physics so many times I struggle with the formulas, such as the ones you threw around like I talk about football scores on Monday morning! But it is good to hear I wasn't missing something.

And Doc, I think what you were getting at is added velocity isn't the "best" or most efficient way to increase bullet rotation, and I would certainly never argue that. Your mention of barrel harmonics is a totally different subject, and affects accuracy independently of bullet stability...meaning, in my mind, a bullet can be "perfectly" stabilized while still showing accuracy differences due to changing powder charges.

I'm sure John could discuss this too death, which I would LOVE to get into, but I doubt it would be very interesting reading for most!

Thanks a lot to both of you!

Dan


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## DuaneinND (Jan 22, 2005)

The formula is: 12x velocity x 60 divided by the twist rate = rpm

SO if a 10 twist barrel works with a 70gr bullet @ 3200 fps

12 x 3200 x 60 / 10 = 230,400 rpm

working backwords with a 12 twist barrel you need 3840fps for the same degree of stability.
However if the same bullet is stable at 2700fps with a 10 twist you could then 3240 fps with a 12 twist will work.
Barrel twist will affect the rpm at a much higher rate than velocity and usually it requires a larger volume case to develop enough velocity to compenate for a slower twist.
As already mentioned the design (shape) of the bullet has more influence than weight. The o'give of the bullet measures the shape of the point, with a 1 being very round and a 10 being very long and pointed. The average hunting bullet is around a 6 and a VLD bullet is 8.5-10. VLD bullets require much faster twist rates to stabilize. Your 12 twist 223 should work with most bullets up to 60 grains and it will also work with the Sierra 63gr semi pointed and the Speer 70gr semi pointed, but the only way to know is to try them. Good luck.


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## Plainsman (Jul 30, 2003)

Duane, good explanation. Twist rate affects things more than velocity, but if anyone has noticed 223 barrels are often 1 in 12 while 22-250 barrels are often 1 in 14.


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## Csquared (Sep 5, 2006)

Hey Duane...can you be my "go to" guy when I'm struggling with one of those formulas?

Please?

But thanks for explaining in detail what we knew, but I, for one could never explain so thoroughly.

Here's one for you, and you can think about it over the holidays....

What is the proper formula to compute recoil with smokeless powder?

Thank you in advance, and MERRY CHRISTMAS!

Dan


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## DuaneinND (Jan 22, 2005)

Dan-Sadly there are more than one way to calculate recoil. Hatcher devotes a chapter to 3 different methods. One of the more simple formulas was worked up by Homer Powley but is based on the use of IMR powders, so it is close.
Add the powder charge in grains to the weight of the bullet in grains, multiply the sum times the powder charge(in grains) and divide the product by 80 times the weight of the gun in pounds.
So if you have a 7# 300 mag shooting a 200gr bullet over 70gr of 4350
70+200=270x70= 18900/ 7x80((560)= 33.75 ft #s
Also in looking for the formulas it was stated that any recoil of 28 ft#s or more was considered to be very uncomfortable for an extented shooting session. So if the above 300 mag weighed 9#s the recoil would drop to 26.25 Ft#s and be much more manageable.

I hope this answers your question.


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## Csquared (Sep 5, 2006)

Thanks Duane, but I'm interested in quantifying the recoil as a force...not the net affect of that force on the shooter, so weight of the rifle (and that of the powder charge, in my mind) is moot. And although the powder charge is easily explained as pertinent to part of the equation, the fact that the differing expansion rates of different powders allows 50 grains of one powder to "push" as hard as 55 grains of another at similar chamber pressures tells me there has to be a "better" way?

Felt recoil formulas are a dime a dozen. I know of none that define "actual" recoil. But since the force inside the barrel is "virtually" the same whether it is taking place inside a barrel attached to a 6 pound rifle, or a several ton boxcar...any formula that requires the weight of the rifle is comparing "felt" recoil.

I realize this is deep, and at the same time a silly waste of time....in some ways. But I could sure end some arguments quick if I could explain it!

And correct me if I'm wrong, but haven't we found since Hatcher's studies that some of his findings are suspect? His explanation of how the velocity of the expanding powder gases relates to the velocity of the bullet comes immediately to mind. I believe we know now it's (gases) much faster than he thought. On a side note, we also can shoot 150gr bullets from a .30/06 much faster now than the 2700fps his research is based on.....for what it's worth.

Anyway, I'm still looking for something other than a felt recoil formula...but I'm not sure you're gonna find it!

But I sure HOPE you do!!!!!!!

Thanks again!


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## DuaneinND (Jan 22, 2005)

I am not sure if I totaly understand exactly what you are looking for, but I will discuss this with both the math and physics instructors at school and see if they have any ideas.
I do know that different powders develop a difference in "felt" recoil. Powders that "build" the pressure curve as the bullet moves down the barrel versus a powder that develops full pressure "instantly" ( not that any take very long with either) seem to kick less, but then that might be because those powders seem to have more of a muzzle "boom" than "bark" and because perchieved recoil is different than measured.
I am wondering if this has to do with the BS thrown out about the WSM cartridges and the various articles trying to sell the concept in where a 6# WSM shooting the same bullet at the same speed as the "old" cartridge in a 2# heavier rifle "seems to kick" less? and the argument that it is using 10 grains less powder that makes up for 2#s of rifle!
I will see if I can find an anwer to the riddle.


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## Csquared (Sep 5, 2006)

The subject has nothing to do with the WSM's specifically...but knowing the answer would also end that discusion too, because they're not using 10 grains less of the SAME powder. If they were, the same bullet would not go the same speed in the same length barrel.......regardless of the shape of the un-burnt powder charge or what letters were stamped on the case head. And until an identicle force is created, regardless of the propellant, identicle bullets don't achieve identicle velocities.....right?

I think you'll find the time aspect of this the most complicated part of the equation, because the force of the expanding gases as smokeless powder burns, the very force we are trying to quantify, is changing every nanosecond. That's where it differs from rocket propulsion theories since there the thrust is produced by a relatively constant propellant.

So see, anyone who's ever said "it's just shooting....not rocket science" wasn't thinking about it enough ! 

But anyway, I'm definitely not a scientist or mathemetician, so my logic could be anywhere from flawed to totally wrong...or somewhere in the middle. But what we know for sure is it's much more complicated than most would initially think upon hearing the question. But I hope you get some answers today, because sometimes it takes a very complicated solution to prevent a simple, but recurring problem.

And this never-ending debate about "what recoils more" is one of those problems.

If you decide to answer in detail perhaps you should do it in another thread as we're totally off subject now.

Thanks again!

Dan


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