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Twist Rate
#1
I would like to pick the minds of those with knowledge again.

This time regarding twist rate.

I know weight of the bullet and twist rate go hand-in-hand.
Is it that heavier bullets need a faster or a slower twist rate?
How do you determine the best twist rate for a certain caliber/grain bullet?
So, knowing the twist rate of my .223, how do I determine the best bullet weight to use.
Same thing for a .30-30, .243, and 7.62x39.

I spoke to one guy that said they were shooting I believe a .223 that the bullets were literally exploding in the air before they arrived at the target due to the bullets being very light weight and the twist rate too fast for them.
He said they got to spinning too fast coming out of the muzzle for how light the bullet was and they basically disintegrated.
Any light you can shed on this subject would be very good.

Thanks.

God bless!!

PPP
Proud to be a member of pa2a.org since 11:18 PM Sept 7, 2012!
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#2
Pistol Packin Preacher;48153 Wrote:I would like to pick the minds of those with knowledge again.

This time regarding twist rate.

I know weight of the bullet and twist rate go hand-in-hand.
Is it that heavier bullets need a faster or a slower twist rate?
How do you determine the best twist rate for a certain caliber/grain bullet?
So, knowing the twist rate of my .223, how do I determine the best bullet weight to use.
Same thing for a .30-30, .243, and 7.62x39.

I spoke to one guy that said they were shooting I believe a .223 that the bullets were literally exploding in the air before they arrived at the target due to the bullets being very light weight and the twist rate too fast for them.
He said they got to spinning too fast coming out of the muzzle for how light the bullet was and they basically disintegrated.
Any light you can shed on this subject would be very good.

Thanks.

God bless!!

PPP

No matter what anybody says here someone else (or others) will debate what is the best twist-rate. Here's one author's opinion from a police magazine/website.

Quote:...What we see today in the LE patrol carbine market is mostly 1/9 or 1/7 twist barrels. So which one is better? For me and my agency it was clear: 1/7. The reason is that the largest consumer of small arms ammo is the military. As such it exerts a great deal of influence over military caliber small arms ammunition development. Two of the best rounds developed in the last few years in 5.56mm have been the 75 grain TAP T-2 and the 77 grain Black Hills Mk. 262. Both of these rounds were developed to work well in 1/7 twist barrels specifically. Accuracy is either inconsistent or nonexistent in 1/9 twist barrels....

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[Image: pa_zps59e4c512.png?t=1379682235]
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#3
Is there a general rule to follow such as heavier bullets slower twist rate or heavier bullets faster twist rate?

Here is what I found on twist rate from Chuck Hawks (http://www.chuckhawks.com/rifle_barrel.htm):

A) It takes less twist to stabilize a given bullet at high velocity than at low velocity.

B) At the same velocity in the same caliber, longer (pointed) bullets require faster twist rates than shorter (round nose) bullets of the same weight.

C) Heavier bullets require faster twist rates than lighter bullets of the same shape. (It is undesirable to spin a bullet a great deal faster than necessary, as this can degrade accuracy.)

D) A fast twist increases pressure and also the strain on the bullet jacket.

Does this appear to match up according to what others have found?
Would anybody add anything to what has been stated?

Thanks.

God bless!!

PPP
Proud to be a member of pa2a.org since 11:18 PM Sept 7, 2012!
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#4
Pistol Packin Preacher;48153 Wrote:...
So, knowing the twist rate of my .223, how do I determine the best bullet weight to use.
...
If you prefer a lot of math, google Miller Twist Rule or Miller Twist Formula.

Empirical data - application is everything.

1:12 was optimized for 55 grain bullet mass used with the M193 ball round (5.56mm military FMJ cartridge). When Uncle Sam increased the bullet mass in the M855 round (62 grains?), it was necessary to increase the barrel twist rate to 1:7 to maintain bullet stability. (details)

My experiences:
To answer your question, and possibly draw fire as an apostate, I still use older 1:12 barrels. Most of the ammunition I use is 55 grain, and this combination works as well today as it did in the 1960s.

I also have a 1:9 barreled upper for heavier bullet configurations, it works for both 55 & 65-ish grain setups. Since it's a short barrel, I haven't done any long range accuracy testing. But I am pleased to report a lack of stability problems with 55 grain from 1:12, and good stability with 55-65 grain bullets from a 1:9 barrel.

So for anyone asking why I'm still using 55 grain: it's cheaper, more common and readily available (details). My application is informal paper target shooting. So, defeating armor, wound ballistics, &c are irrelevant.

More information:
  • http://kwk.us/twist.html
  • http://en.wikipedia.org/wiki/Twist_rate#Twist_rate
  • http://www.barnesbullets.com/images/223RemingtonWeb.pdf
  • http://www.californiapredatorsclub.com/index.php?showtopic=7179

Clicking on each image should backtrack to the source.

[Image: twist180.png]

[Image: post-6071-0-19340200-1344589687.jpg]


[Image: 42274d0c.png]

[Image: twist.gif]


Typos.
Subject matter expert on questions no one's asking.
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#5
Bullet length also affects how twist rate will impact the performance of the round, so it isn't just about weight.

[Image: 21122657_10155704889299275_8952212329936901321_o_2.jpg]
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#6
ShaulWolf;48575 Wrote:Bullet length also affects how twist rate will impact the performance of the round, so it isn't just about weight.

^^^^^^TRUTH^^^^^^^^^

It's not weight, it's length. Military sometimes uses steel care rounds which are longer than their lead core counterparts. Tracer rounds are also longer. That's why they need more twist. Every 1:9 I ever had would stabilize a 77gr ball.

STABILITY CALCULATOR
lycanthrope, proud to be a member of pa2a.org since Sep 2012.
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