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Offline searlock

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twist rate
« on: October 28, 2009, 02:51:33 AM »
i have been looking at twist rates and i can't understand some changes that have been made in handies. in the 223 i see people saying 5 grains of bullet weight change can make a big difference in group size. i see that in the 06 that 1 in 10 is standard in most barrels and has been for a long time. bullet weight ranges from about 110 gr to 220 gr and thats a large difference in weight. in the handi 444 marlin the twist rate has been changed from 1 in 38 to 1 in 20 and that is a huge difference. my question is if the 1 in 20 is so right then how could the 1 in 38 have been so wrong? i see that velocity has nothing to do with it because the 30-30 handi is 1 in 10 and the 300 wby mag is 1 in 10 big difference there, same bullet. is bullet shape more of a factor on group size in bullets of the same weight with a given twist rate such as the 30-30 110 gr speer rnsp as opposed to the speer 110gr spire sp? reason i ask is because i can't change the twist rate in my barrels, only the bullets.
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Offline mitch132

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Re: twist rate
« Reply #1 on: October 28, 2009, 04:44:29 AM »
Try researching the Greenhill Equation. Stability of a bullet in flight is a function of velocity, length, and rate of twist in the barrel. Varying the bullet weight is a way of changing its length since the diameter is constant. This is also why two bullets of the same weight, fired at the same velocity, and through the same twist rate barrel may shoot differently, where the round nose flat base one may stabilize and the pointy VLD boat tail one might not.

http://en.wikipedia.org/wiki/Rifling <-- Scroll down to the section on Twist Rate

http://kwk.us/twist.html <-- Online calculator
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Offline dieselten

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Re: twist rate
« Reply #2 on: October 28, 2009, 05:19:41 AM »
It is not really the bullet weight you should be concerned with (regarding stability) as much as the LENGTH of the bullet.  People over simplify by saying heavier bullets need faster twist when in reality LONGER bullets need a faster twist. 

The reason 10 grains in .22 caliber makes a significant difference is because that is approx. 20% of the total weight and even more importantly the length increases significantly.  Whereas 20 grains in a 44 Mag is only about 8% and the increase in length is very minimal.

You can use heavier bullets with the same twist by doing two things:
- use a bullet with short length (no boat tails)
- increase velocity

The reason all Handi .30 rifles are 1-10" is simply to save money and it works because accuracy does not suffer accross all calibers.  Whereas in .22 you have a much wider range of velocities & bullets to accomodate - .22 Hornet to .220 Swift or .22-250.
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Offline JerryKo

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Re: twist rate
« Reply #3 on: October 28, 2009, 06:18:16 AM »
EXCELLENT Reply!

Jerry
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Offline GrampaMike

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Re: twist rate
« Reply #4 on: October 28, 2009, 07:51:44 AM »
FYI:



BD = Bullet Diameter (inches)
BL = Bullet Length (inches)
BW = Bullet Weight (grains)
RT = Rate of Twist (for example: 1 in 10 = 10)
MV = Muzzle Velocity (feet per second)
SF = Stability Factor (1.5 is considered to be fully stabilized)



If you know BD, BL, BW, RT and MV the formula for SF is:

SF=((BW*(20.62*(BD^2.25))^2)/((RT*(BL^2.25))/(1-(MV/5705))



If you know BD, BL, BW and RT the formula for minimum MV needed for a fully stabilized bullet is:

MV=5705*(1-((BW*(20.62*(BD^2.25))^2)/(RT*(BL^2.25))^2)/1.5)



If you know BD, BL, BW and MV the formula for RT needed for a fully stabilized bullet is:

RT=(20.62/((BL/BD)^2.25)*SQRT(BW/((1-(MV/5705))*1.5)))



Mike
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Offline quickdtoo

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Re: twist rate
« Reply #5 on: October 28, 2009, 08:08:09 AM »
If you care to rely on the Greenhill forumula which has it's issues, here's a handi twist rate calculator.

http://kwk.us/twist.html

And another

http://www.uslink.com/~tom1/twistrate.htm

And the Miller formula...

http://accurateshooter.wordpress.com/2008/06/03/calculating-bullet-rpm-spin-rates-and-stability/

Tim
 



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Offline peternap

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Re: twist rate
« Reply #6 on: October 28, 2009, 02:39:59 PM »
Quote from: quickdtoo on October 28, 2009, 08:08:09 AM
If you care to rely on the Greenhill forumula which has it's issues, here's a handi twist rate calculator.

http://kwk.us/twist.html

And another

http://www.uslink.com/~tom1/twistrate.htm

And the Miller formula...

http://accurateshooter.wordpress.com/2008/06/03/calculating-bullet-rpm-spin-rates-and-stability/

Tim
 





Here's an online bullet calculator. I've been using it a lot lately making bullets for the 12 ga. It's pretty accurate. Play with the variables and ee for yourself.

http://www.uslink.net/~tom1/twistrate.htm
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Offline quickdtoo

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Re: twist rate
« Reply #7 on: October 28, 2009, 02:45:54 PM »
Ummm, that's one of my links, glad it works for ya tho, they may already be in the FAQs, I've forgot half the stuff that's been put there over the years!  ;)

Tim
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Offline searlock

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Re: twist rate
« Reply #8 on: October 28, 2009, 03:15:21 PM »
guys naught times naught = naught is about as far as my math skills go, but i can put two holes close together on paper. now you all have answered my question about mv and bullet size but i still don't know why the 444 handi was changed from 1in38 to 1in20. my old speer manual shows the 444 at 1in38 and if it is correct as the kwk.us/twist.html plug in chart showed it to be with the speer 300gr ucsp how can it work with a 1in20 twist? also for this chart to work with my 500 smith the bullet would have to be over 2 inches long out of my handi and that ain't gonna work.
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Offline quickdtoo

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Re: twist rate
« Reply #9 on: October 28, 2009, 03:32:35 PM »
Marlin switched to 1:20" in all of their .444 rifles including the H&R .444 which is made by Marlin. Here's a recent thread in the Marlin Levergun forum on the .444 with some links on shooting big bullets in the .444. I've shot the 355gr Beartooth in my H&R .444, it shoots real good, I've also shot the 700gr Ranger Rick's in my .500S&W H&R, they shoot about the same as everything else I've shot in it, ~2" at 100yds. Tyler shot the 720gr Ranger Rick's in his 45-120 which keyholed at the velocity he shot them at which I don't recall right off, we figured he's have to push them around 1800fps to stabilize in the 1:20", I never sent him any more of those monster bullets cuz he would've shot them and probably hurt hisself!! :o

Tim

http://www.gboreloaded.com/forums/index.php/topic,178409.0.html
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Offline searlock

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Re: twist rate
« Reply #10 on: October 28, 2009, 04:03:33 PM »
well i now understand about the heavy cast bullets in the 444 and i never really concidered them because i don't shoot cast bullets and they are not listed in my old speer manual. so i expect the 300gr ucsp would be fine in the 1in38 barrel, don't know about the 1in20 barrel for the same bullet. so far the biggest jacketed bullet i have found for my 500 handi is the 500gr hornady and it seems to do the best but i am soon to start reloading for it and i will know more then. thank for the info all, especially the baretooth article.
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Offline Default

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Re: twist rate
« Reply #11 on: October 29, 2009, 08:37:51 AM »
Sear ,

 We need to get you a couple more manuels then ... Lees second edition would be welcomed i would think ... Also check out IMR powders website ... They have their load data center , It is rather nice to have when comparing data since it listed loads using Winchester, Hodgon and IMR powders in whatever caliber you are reloading ... My old man has a old speer manuel and i plan on getting him a couple more , Its always nice to be able to cross refference load data between different sources... But the IMR load data will help you out considerable so that you have more load data options then speer gives , since speers data caters to just their bullets ....  http://www.imrpowder.com/


   Hope this helps ....

    Default
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Offline searlock

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Re: twist rate
« Reply #12 on: October 29, 2009, 11:50:47 AM »
would like to get some more manuals but can't do it right now.
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