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What TWIST RATE for which bullet weight

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Category: Firearms, Bows, and Ammunition
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Forum Description: Anything to do with ammunition
URL: http://www.opticstalk.com/forum_posts.asp?TID=19347
Printed Date: December/17/2018 at 01:08


Topic: What TWIST RATE for which bullet weight
Posted By: Urimaginaryfrnd
Subject: What TWIST RATE for which bullet weight
Date Posted: September/19/2009 at 17:18

BULLET WEIGHT / CALIBER / TWIST RATE CHART

Grain/Cal .172 .204 .224 .243 .257 .264 .277 .284 .308 .338 .358
17-20 9-10                    
25 10                    
30 9 12                  
33   12                  
35   12                  
37 VLD 6                    
40   12                  
50-52   9 14                
55     12                
60     12                
68-69     9,10 13,14              
75     9   14            
80     8                
85     7 12 12 12          
90     7 10              
100       10 10   12 14      
105-107       8              
120         10 10   12 15,16    
130             10   14    
140           9 10 10      
150                 14    
140-160           8 10 10 12,13    
150-168               9 11,12,13    
150-180                 10,11,12    
160               9      
175               9      
180                 10,11,12    
200                 10,11 10,12 12,16
220                 10    
225                   10,12 12,16
240-250                 10 10 12
300                   10 12


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"Always do the right thing, just because it is the right thing to do".
Bobby Paul Doherty
Texas Ranger



Replies:
Posted By: lucytuma
Date Posted: September/19/2009 at 17:56
Good chart Wes, should be usefull to many.

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"The democracy will cease to exist when you take away from those who are willing to work and give to those who would not." - Thomas Jefferson


Posted By: cheaptrick
Date Posted: September/19/2009 at 18:35
Thanks, Wes.


Posted By: sakomato
Date Posted: September/19/2009 at 21:12
What!  No 375!  Shocked
 
 
Just kidding, thanks


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Guns only have 2 enemies, rust and politicians


Posted By: 300S&W
Date Posted: September/20/2009 at 07:31
  Or 9.3?  Just funnin' to.  Got the chart in my FAVORITES already.

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"I ain't got time to bleed!"


Posted By: Clark
Date Posted: September/21/2009 at 13:20
If I chamber a 1 in 16" twist 22 rimfire barrel in .223, the 55 gr bullets will not stabilize, but the 50 will, at least out to 100 yards.

We usually wind up using the 33 gr Vmax at 3500 fps is very good out to 180 yards.

That twist is off the chart.


Posted By: mike650
Date Posted: September/21/2009 at 13:45
Thanks Wes!!!  Excellent

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Fish to Live, Live to Hunt


Posted By: matc
Date Posted: September/21/2009 at 16:13

thanks

I was just looking for somthing like thatBig Grin 

matt


Posted By: SD Dog
Date Posted: September/21/2009 at 16:26
Thunbs Up


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If nobody ever said anything unless he knew what he was talking about, a ghastly hush would descend upon the earth. AP Herbert

Stupidity & ignorance have been the foundation for many certainties.


Posted By: Monster
Date Posted: September/21/2009 at 16:28
Question I have a 1:9 twist rate in my 223. Would I be better of shooting 68 gr. bullets as opposed to 50 or 55?

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"Get Busy Livin' or get busy dyin'" -Red (Shawshank Redemption)


Posted By: matc
Date Posted: September/21/2009 at 19:04
monster I was using the 50 gn v-max in the same barrel as you and it was shooting very good ouder a 1/2 IN but I found out that at 200 yard I had a hard time geting a 3 IN group also I had a very bad copper build up. I think that the twist was to much for the bullet . I will be going back to the larger bullets.  matt


Posted By: supertool73
Date Posted: September/21/2009 at 19:28
I shoot 55 grains out of my ARs with 1-9s all the time and they shoot good.  I have even shot 55s in the 1-7 and they do okay.

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Lifetime warranty and excellent customer service don't mean a thing when your gun fails during a zombie attack.

"A Liberal is a person who will give away everything they don't own."


Posted By: RONK
Date Posted: September/21/2009 at 22:03
 I've shot bullets as light as 40 grains out of a 20", 1-9 .223. Sub-minute to maybe 300 yards (?) if the wind doesn't get ahold of them.
 It also handles 75 Hornady HPBTs very well, but NOT the 75 A-Max's!
They group lousy anywhere from the muzzle forward, but my cousin's 1-7 shoots them just  fine. I've never tried 77 or 80 Sierras in my 1-9,  but I wouldn't be surprised at rather dismal results with either. Most guys seem to need at least a 1-8 for those, at least in the .223.


Posted By: boliodogs
Date Posted: October/04/2009 at 15:31
That is a very useful chart. Thanks.


Posted By: biggreen747
Date Posted: October/17/2009 at 10:06
I'll throw in my .02 here as well and some of you really smart guys please correct me if I am wrong.. While we use bullet weight as a general guide it is really the length of the bullet that determines the twist rate required. All copper bullets such as the Barnes, Hornady GMX, and Nosler E-tip must be longer to achieve the same weight as a comparable lead core bullet and therefore one of these bullets that is equal in weight to a traditional bullet may not stabilize in a given twist rate. I have a 7mm RM that is a good example of this. The rifle has a 1-9 1/2 twist and will stabilize a traditional 145/150gr bullet just fine but will not stabilize a 150gr Barnes TSX. 

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We measure it with a micrometer, mark it with a crayon, and cut it with a chainsaw.


Posted By: okc4956
Date Posted: October/18/2009 at 00:09
biggreen is right. it's more a function of length as wieght. i've got an excel spreadsheet that will tell you the optimum twist rate after you put in your bullet dimensions, but the problem is you can't easily alter your twist rate. This chart is about as good as anything I've seen. American Flag Very good ball park numbers I'd say.


Posted By: pyro6999
Date Posted: October/18/2009 at 21:05
this chart is from dan lilja's web site i believe. i printed a copy out and keep it near my computer.

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They call me "Boots"
375H&H Mag: Yeah, it kills stuff "extra dead"

343 we will never forget

God Bless Chris Ledoux
"good ride cowboy"


Posted By: 0311GRUNT
Date Posted: November/28/2009 at 23:59
Originally posted by Monster Monster wrote:

Question I have a 1:9 twist rate in my 223. Would I be better of shooting 68 gr. bullets as opposed to 50 or 55?

I shoot 55 Gr out of my 1/7 and 69gr out of my 1/9 and both hold sub moa at 100 and 1 moa at 300


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You cant hit what you cant see


Posted By: SVT_Tactical
Date Posted: December/21/2009 at 09:06
it so un-uniform as to what gun likes what bullet best or what twist rate stabalized a 70gr best or what twist do I need to shoot a 168gr best.  The only way, and i repeat, only way to know what works best in your gun is to actually shoot it and test.  Example, i ordered two identical 24" barrels for myself and a friends AR to do an upper build.  Both put together by the same builder using the same headspace guages and mine puts the 75g A-max in the same dang hole almost at 100 yrds.  His can't get better than 1".  Even when I shoot both.  He can get best results from a sierrra 80gr where i get get anything them to group worth a crap.  So again. test and when you find a bullet weight that works keep plenty on hand because you know it works.  Then as you have time (and money) get some small boxes of other bullets and see if they compare.  A good method and what I have done in the past was load different gr bullets with a charge that would be safe for all and shoot them to 100yds.  whichever gr. bullet gave the best group I started to work the charge on until i got the best groups i could. 


Posted By: cowski
Date Posted: January/16/2010 at 23:31
i have a 9 in twist will it work with 77 gr sierra's?


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never corner something meaner than you are jbc


Posted By: Urimaginaryfrnd
Date Posted: January/17/2010 at 01:49
http://le.atk.com/pdf/223_MinimumTwistRates.pdf - http://le.atk.com/pdf/223_MinimumTwistRates.pdf     Your best performance will be with bullets no longer than .829 inch with a 1:9 twist.   The 69 gr bullet is .900 I would suggest you measure the length of the 60 gr AMAX Horniday and try that fot the 1:9 twist.
 
You can shoot the 77 but it may not be as tight as it would with something in the 55 to 60 grain weight.   Try it and see what you get.  Note some 75 and heavier bullets have to be single shot loaded especially the 80 gr.
http://www.whiteoakprecision.com/info-reloading.htm - http://www.whiteoakprecision.com/info-reloading.htm


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"Always do the right thing, just because it is the right thing to do".
Bobby Paul Doherty
Texas Ranger


Posted By: RONK
Date Posted: January/17/2010 at 11:32
Originally posted by cowski cowski wrote:

i have a 9 in twist will it work with 77 gr sierra's?
 Could go either way.
Shoot them to find out. It's the only way to know.
 You're on the borderline though, in my estimation.


Posted By: koshkin
Date Posted: January/17/2010 at 14:30
Originally posted by RONK RONK wrote:

Originally posted by cowski cowski wrote:

i have a 9 in twist will it work with 77 gr sierra's?
 Could go either way.
Shoot them to find out. It's the only way to know.
 You're on the borderline though, in my estimation.

77gr is a little heavy for 1 in 9 twist.  It might work well, but chances are you will do better with a lighter bullet.  My 1 in 9 twist 223 seems to really like 69gr SMKs.

ILya


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Posted By: GetSome
Date Posted: January/17/2010 at 14:40
I would like to try some 77 gr. in my .223  1in8...does the military use sierra?  And I would assume it would have to have a cannalure, so is that set back far enough to allow a  crimp and still feed through a mag without single loading...I would imagine it would have to.  Any info you have would help I don't know anyone I could ask about the 77s locally.


Posted By: koshkin
Date Posted: January/17/2010 at 15:45
Originally posted by GetSome GetSome wrote:

I would like to try some 77 gr. in my .223  1in8...does the military use sierra?  And I would assume it would have to have a cannalure, so is that set back far enough to allow a  crimp and still feed through a mag without single loading...I would imagine it would have to.  Any info you have would help I don't know anyone I could ask about the 77s locally.

I am pretty sure there are two varieties of 77gr SMKs: with cannelure and without it.  I have only used the ones without cannelure, so I can't comment on the other ones.

ILya


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http://www.opticsthoughts.com - www.opticsthoughts.com
http://fb.me/DarkLordOfOptics - Facebook
The greatest obstacle to discovery is the illusion of knowledge


Posted By: Dale Clifford
Date Posted: January/17/2010 at 17:54

note -- one of the inputs is length

http://www.jbmballistics.com/cgi-bin/jbmstab-5.0.cgi - http://www.jbmballistics.com/cgi-bin/jbmstab-5.0.cgi


Posted By: Dale Clifford
Date Posted: January/17/2010 at 17:58
yes the military uses the smk for the long range load. the bc is still only around .4 so wind drift is still a factor, especially when the load is shooting below 3000 fps.


Posted By: scooter65
Date Posted: January/24/2010 at 08:56

Great chart Wes... I was just looking for a cross reference chart like this and walla!  I couldn't find the link online for it.  I captured the chart image in a .jpg file if anybody would like it so they can just print the chart off. 

http://www.opticstalk.com/uploads/4389/twistrate.zip - uploads/4389/twistrate.zip


Posted By: pyro6999
Date Posted: January/24/2010 at 11:53
lilja barrel company has a very nice chart as well, i have a copy of it printed out that i keep near my computer so when im looking at rifles and potential bullet combos in those rifles i can look at the twist rates and decide if its worth a shot or not.
http://www.riflebarrels.com/products/caliber_twist_rates.htm - http://www.riflebarrels.com/products/caliber_twist_rates.htm


-------------
They call me "Boots"
375H&H Mag: Yeah, it kills stuff "extra dead"

343 we will never forget

God Bless Chris Ledoux
"good ride cowboy"


Posted By: scooter65
Date Posted: January/24/2010 at 12:46
Originally posted by pyro6999 pyro6999 wrote:

lilja barrel company has a very nice chart as well, i have a copy of it printed out that i keep near my computer so when im looking at rifles and potential bullet combos in those rifles i can look at the twist rates and decide if its worth a shot or not.
http://www.riflebarrels.com/products/caliber_twist_rates.htm - http://www.riflebarrels.com/products/caliber_twist_rates.htm
 
THANKS!  Saved to my favorites list now.


Posted By: koshkin
Date Posted: January/24/2010 at 18:19
Berger Bullets website lists the recommended twist rate for every bullet they make.

ILya


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The greatest obstacle to discovery is the illusion of knowledge


Posted By: trigger29
Date Posted: January/24/2010 at 19:23
Originally posted by Dale Clifford Dale Clifford wrote:

note -- one of the inputs is length

http://www.jbmballistics.com/cgi-bin/jbmstab-5.0.cgi - http://www.jbmballistics.com/cgi-bin/jbmstab-5.0.cgi
Dale, I noticed that the stability factor changes with velocity. We all know that bullets don't stay the same velocity after they leave the barrel, so I was wondering, if your velocity is 2900 with a stability factor of 1.135 What happens when the bullet gets to 1900 fps, and the stability factor drops to .986. Will the bullet destabilize, and start to tumble or wobble?

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"A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."


Posted By: The Apostle
Date Posted: February/13/2010 at 02:13
I'm going to get some bulk Federal Gold Medal Match in .308 Win...my Ruger is 1:10 twist...Which would suit my rifle best...168gr?...175gr?...or both???


Posted By: SVT_Tactical
Date Posted: February/13/2010 at 08:09
Normally the faster twist will stablize a heavier bullet.  I would try both to see which provided better accuracy, if they are equal then get teh 175. It will fight the wind better than the lighter grain.  With a 10 twist you may even be able to put some bullets up to 200gr or even the 208 hornady a max.  I know this doesn't really answer your question so if I had to say one of the two it would be the 175 because of wind drift


Posted By: Urimaginaryfrnd
Date Posted: April/25/2010 at 20:43
Salute

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"Always do the right thing, just because it is the right thing to do".
Bobby Paul Doherty
Texas Ranger


Posted By: 300S&W
Date Posted: April/25/2010 at 21:01
 Anyone familiar with this:
 
  http://stevespages.com/page8e.htm - http://stevespages.com/page8e.htm


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"I ain't got time to bleed!"


Posted By: budperm
Date Posted: May/06/2010 at 07:31
Interesting link Earl!  I will have to save it and study it when I have more time!

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"Peace is that brief glorious moment in history when everybody stands around reloading".
--Thomas Jefferson





Posted By: 300S&W
Date Posted: May/06/2010 at 07:33
  Worked for me when I had to decide what rate of twist I wanted my 9.3 rebored to. Ended up at 1-12.

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"I ain't got time to bleed!"


Posted By: Bigdaddy0381
Date Posted: May/18/2010 at 09:20
Originally posted by trigger29 trigger29 wrote:

Originally posted by Dale Clifford Dale Clifford wrote:

note -- one of the inputs is length

http://www.jbmballistics.com/cgi-bin/jbmstab-5.0.cgi - http://www.jbmballistics.com/cgi-bin/jbmstab-5.0.cgi
Dale, I noticed that the stability factor changes with velocity. We all know that bullets don't stay the same velocity after they leave the barrel, so I was wondering, if your velocity is 2900 with a stability factor of 1.135 What happens when the bullet gets to 1900 fps, and the stability factor drops to .986. Will the bullet destabilize, and start to tumble or wobble?
 
 @50 yards this .243 with a 115gr berger it shot fine under1/2 group, now @100 the hit side ways. I'm not sure of the FPS on this load but as it slowed just a tad it started to flip. I guess most if it would depend on the bullet itself. as it might just have a yaw and not tumble. i want to say this is from a 1-10. I went with a 95gr for this rifle and it loves them out to 500 so far.
 
See they hit side ways.
 
 


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P&Z Firearms , Pro gun cleanings and gun repair and wood refinishing.

Ecclesiastes 10:2


Posted By: Dale Clifford
Date Posted: May/19/2010 at 08:01
while  the bullet decreases in speed, the rotational rate stays the same, so the amount of revolution per unit of distance traveled remains the same it takes more time to do it at the slowed velocity rate. Upon firing the base of the bullet is accelerated faster than parts of the bullet above this, (obtruation sp?). the more weight in the back causes better bc, but also gives more of shuttlecock effect. HBWC are an extreme example. At some point a bifurcation or change of a parameter in the relation between the inertial masses  of the front and back and the tumbling occurs. Pitch and yaw are different.


Posted By: Bigdaddy0381
Date Posted: May/19/2010 at 08:07
Originally posted by Dale Clifford Dale Clifford wrote:

while  the bullet decreases in speed, the rotational rate stays the same, so the amount of revolution per unit of distance traveled remains the same it takes more time to do it at the slowed velocity rate. Upon firing the base of the bullet is accelerated faster than parts of the bullet above this, (obtruation sp?). the more weight in the back causes better bc, but also gives more of shuttlecock effect. HBWC are an extreme example. At some point a bifurcation or change of a parameter in the relation between the inertial masses  of the front and back and the tumbling occurs. Pitch and yaw are different.
 
So a 1-10 twist stays 1-10 regaurdless of fps?
 

Dose obturation effect the flight of the bullet?

 

 
 


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P&Z Firearms , Pro gun cleanings and gun repair and wood refinishing.

Ecclesiastes 10:2


Posted By: Dale Clifford
Date Posted: May/19/2010 at 11:17
the spin rate doesn't slow down like the fps rate (more accurately -- the differential rate of change is considerably less, and the time or space constant can be ignored to linerize the problem). Obturation sets the conditions, if the bullet doesn't seal, gas blow by will tip the bullet on exit.
Especially true with cast bullets and alloy types. Yaw and pitch are oscillations or periodic sine waves that occur when position and time are plotted that occur. Bifurcation happens when the center of mass is moved thru the axis of the bullet and at some point the system falls apart and into an "attractor" of more stability.


Posted By: budperm
Date Posted: May/19/2010 at 11:28
What did he just say?!?!?   I think he is a closet lawyer.
 
 
I followed some of that but most went over at a rather high altitude. Clown


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"Peace is that brief glorious moment in history when everybody stands around reloading".
--Thomas Jefferson





Posted By: Dale Clifford
Date Posted: May/19/2010 at 11:42
Numerical analysis can have different forms. When its used with ballistics as we talk about the calculations are done with numerical integrators using first order linear differential equations, that when plotted against each other, (the first matrix is time, the second is trajectory, etc, depending on the variable input) gives the plots and figures seen in places like JBM and Sierra. Usually a system (control systems) methodology isn't used because it gives other types of information, (such as the above) which doesn't really help someone hit something. A similar example is thinking of bullet energy (in terms of classical mechanics) as opposed to thermodynamics. Each give different information because the approach is different.


Posted By: Bigdaddy0381
Date Posted: May/19/2010 at 11:47
[QUOTE=Dale Clifford]the spin rate doesn't slow down like the fps rate (more accurately -- the differential rate of change is considerably less, and the time or space constant can be ignored to linerize the problem). Obturation sets the conditions, if the bullet doesn't seal, gas blow by will tip the bullet on exit.
Especially true with cast bullets and alloy types. Yaw and pitch are oscillations or periodic sine waves that occur when position and time are plotted that occur. Bifurcation happens when the center of mass is moved thru the axis of the bullet and at some point the system falls apart and into an "attractor" of more stability.
[/QUOTE]
Good point I didn't think of it that way. I was thinking more of the base of the bullet would go to one side or the other and not have a even base/contact. like 40% to 60% bottom would make the bullet wobble when it slows. Like out running a tire wabble on the high way. feel it slow and you don't when you speed up.
 
At what rate do you think or see it slowing too? If I can find the email from a controled test I'll post it. from the test it showed the rotation slowed as the velocity slowed and the twist stayed the same. Let me do some digging..
 
 
 
 
 


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P&Z Firearms , Pro gun cleanings and gun repair and wood refinishing.

Ecclesiastes 10:2


Posted By: Dale Clifford
Date Posted: May/19/2010 at 17:00
ask the question from a different view-- what drag forces are acting on the rotational spin?


Posted By: pyro6999
Date Posted: May/19/2010 at 21:28
Get Your Popcorn Ready i need some aleve

-------------
They call me "Boots"
375H&H Mag: Yeah, it kills stuff "extra dead"

343 we will never forget

God Bless Chris Ledoux
"good ride cowboy"


Posted By: trigger29
Date Posted: May/20/2010 at 07:36
It seems to me that if a bullet is stabilized when it leaves the barrel, it should stay that way as long as no outside force interrupts it. The bullet's velocity will bleed off fairly fast, where as the rotational force should not lose it's speed nearly as fast...........Or I'm way off base, and as usual don't know what I'm talking about.

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"A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."


Posted By: Bigdaddy0381
Date Posted: May/20/2010 at 08:23

The twist has to slow some. The ojive has a bearing surface that has an extreme force pushed upon it. I agree it will not slow as fast as the velocity but it slow to where the twist rate stays the same. If it didn't the twist rate would speed up. Say a 1-10 at 3,000 fps @ 20yards and a 1-5 at 1,500 @ 800yards if the twist didn't slow when shot from the same rifle. It’s easier to say than type.

 



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P&Z Firearms , Pro gun cleanings and gun repair and wood refinishing.

Ecclesiastes 10:2


Posted By: cyborg
Date Posted: May/20/2010 at 10:37
Air has a mass, and as such forces friction upon things moving whether they are spinning or moving in a path. That affect is a constant. The bullet will lose spin at a proportional rate that it loses forward movement so long as it remains in flight..

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Posted By: Dale Clifford
Date Posted: May/20/2010 at 20:22

here is a good article if interested.

http://www.nennstiel-ruprecht.de/bullfly/ - http://www.nennstiel-ruprecht.de/bullfly/ http://www.nennstiel-ruprecht.de/bullfly/micro.htm#header_microscale -


Posted By: Sgt. D
Date Posted: May/20/2010 at 21:00
Originally posted by pyro6999 pyro6999 wrote:

Get Your Popcorn Ready i need some aleve
.
 
 
 


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Take care of Soldiers, Show em how its done and do it with em, Run to the Fight & and hold your ground! I die my men go home! If you're a NCO and this ain't you. GET OUT! GOD BLESS AMERICA!


Posted By: pyro6999
Date Posted: May/20/2010 at 21:03
you got it D!

-------------
They call me "Boots"
375H&H Mag: Yeah, it kills stuff "extra dead"

343 we will never forget

God Bless Chris Ledoux
"good ride cowboy"


Posted By: Stevey
Date Posted: July/30/2010 at 02:04
SmileThe Sierra manual has some charted data showing the effects of twist rates on bullets. For example, a chart shows the effects of twist rates on their 69 grain .224 MK affecting measured ballistic coefficents. This chart shows a 1-7 twist results in the most uniform b.c. 1 in 12 twist makes for b.c.'s that not uniform.
 
The 190 grain .308 MK seemed to like 1-10.
 
As the projectile is launched out of the barrel a number of factors come into action such as yaw and precess (sp?). Play around with a gyroscope and push it to one side and it will move at right angles -- in a bullet this is called "coning". Anyhow, if I want one hole groups at 100 yds I shoot short bullets with a slow twist. If I want to hit far away targets when the wind is blowing I shoot long pointy bullets that need a fast twist. I cannot remember shooting tiny groups with my 6.5-06 using 142 Si MK's (1-8 twist).
 
The Sierra manual has numerous diagrams that show what happens when a bullet is launched down range (force and direction or vectors) - terms such as yaw, deflection, center of mass, center of pressure are described. The diagrams show what occurs. An anaysis of the situation using first order dif equations or thermodynamics would bring me back to my class room days when I could not afford rifles and had no time for shooting.


Posted By: Stevey
Date Posted: August/01/2010 at 23:40
SmileIs obduration the increase of the base area of a bullet caused by expanding gas pressures caused by burning gun powder? My guess would be that most jacketed rifle bullets would have zippo obduration but civil war era mini ball type projectiles would have the most. Miking my boat tail jacketed rifle bullets dug out of snow banks seems to indicate no change from bullets out of the box, except for rifling marks, from the snow bank bullets.
 
I would guess that shooting tiny groups such as in bench rest competion is somewhat of an art and maintaining a small variation in ballistic coefficients by selecting the proper twist rate is only part of the problem. Bench rest competion at 100 yards with a 6mm PPC with 75 grain bullets would be different than bench rest shooting at 1000 yds with a 6.5-.284 with 140 -142 VLD bullets. Switch rifles for each event and realize a zippo score.
 
If in doubt go for the faster twist.


Posted By: Dale Clifford
Date Posted: August/02/2010 at 08:48
It occurs because of the differences in the moment of interia within the body of the mass. The more mallaeble the material the more obtruation. In softer lead bullets the base is accelerated faster than the front  filling in the lands. If the acceleration is hard enough the bullet will strip instead of spin and lead is left in the barrel. Gas checks are added to stop this and gas blow by. All real life stuff when accelerated exhibit set back. Sometimes its better study these under conditions called elastic collisions, when some of the conditions are relaxed. (atomic particles) Even soft lead bullets when recovered in a snow bank will show no differences when miked out.
most shooting sports are the antithesis of bench rest shooting. In real life shooting very little observable differences occur when the bc of bullets only varies by a factor of .05. Faster twist barrel will always have the trade of more wear and lower velocity.
There have been quite a few long range records set with non boat tail seemingly high drag bullets, and I shoot sub moa groups all the time with boat tails (as do others) at 100 yds. Most of the differences in bench rest come from the different guns, and its a reloading sport as much as a shooting sport.


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I love little league baseball-- it keeps the kids out of the house
Yogi Bera



Posted By: Kickboxer
Date Posted: August/02/2010 at 12:10
Hey, what about .458 and .510????  
I see some discrimination here...

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Opinion,untempered by fact,is ignorance.

There are some who do not fear death... for they are more afraid of not really living


Posted By: Dale Clifford
Date Posted: August/02/2010 at 12:20
Not at all --- long range shooters at Raton NM use 45 sharps etc. for 1000 yds and longer and none of their bullets are pointy.

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I love little league baseball-- it keeps the kids out of the house
Yogi Bera



Posted By: Gunshow75
Date Posted: August/03/2010 at 18:48

[/QUOTE] Dale, I noticed that the stability factor changes with velocity. We all know that bullets don't stay the same velocity after they leave the barrel, so I was wondering, if your velocity is 2900 with a stability factor of 1.135 What happens when the bullet gets to 1900 fps, and the stability factor drops to .986. Will the bullet destabilize, and start to tumble or wobble? [/QUOTE]

I assume you are inquiring about the stabilty factor for the bullet at a point down range when it has slowed to 1900 fps.  If so, the stability factor does not get smaller; it is actually larger.   
 
I think you are discussing the gyroscopoic stability factor (GSF) at the muzzle.  If we define the stability factor at the muzzle to be S, the more general equation for the stability factor is S * (Vm/V)^2, where Vm is the muzzle velocity and V is the velocity at any point down range.  The stability factor is lowest at the muzzle, and that is where the value for the twist is determined.
 
Since there were also inquiries about bullet RPM, the general equation is also proportional to spin rate.  Spin rate decreases as the bullet goes down range, but it decreases much more slowly than the bullet's forward velocity decreases. 


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Tom





Posted By: Kickboxer
Date Posted: August/03/2010 at 20:45

Great explanation, Tom...



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Opinion,untempered by fact,is ignorance.

There are some who do not fear death... for they are more afraid of not really living


Posted By: Stevey
Date Posted: August/27/2010 at 01:38
SmileYes, boat tail bullets can shoot sub MOA @ 100 yds but bench rest matches require better than that. A 70 gr 6mm PPC can kill small bugs at 100 yds.  A 45-70, 300-500gr. can make it out to 1000yds but at that range it has been sub sonic for almost half its flight (blooby trajectory). Help me out on this ... is Hookes law, as pertaining to the elastic qualities of metals ? (bullets in snow banks) causing the bullets to contract after being obdurated by either expanding gasses (rapid pressure increase) or differences in acceleration forces applied to the end of the bullet as opposed by the other pointy end that is at rest at the start of acceleration from say 0 to over 3000 fps. Is a stubby mini ball with its hollow base puffed up by a blast of black powder? Has anybody ever seen signs of gas blow by from firing a tightly fitting jacketed rifle bullet through a precisely matched rifle bore? My guess is they either slide through cleanly or get stuck -- possibly there is no room for obduration.
 
If in doubt go for a faster twist. 
My feeling is that B.C.'s vary with velocity as much as 10% (or possibly more) due to primarily coneing and any effect due to obduration is zippo as acceleration stops after the bullet is launched and providing the elastic properties of the bullet are not exceeded the bullet assumes it's prelaunch diameter except for rifling and other marks.
 
I have 2, 1-8 twist .243's that shoot 107 & 105 gr boat tail bullets just fine -- even up to 1000yds but I have not been able to hit a small bug at 100 yds with either of them. I would guess a 1-8 twist would be marginal with 115, 6mm's and 1-7 would be better  -- the observation of keyhole's at 100 yds and not at 50 yds is of note, I guess things just keep on going bad down range.
 
 I have noticed the groups fired with 142 gr SiMK (1-8 twist) at 100 yds are only moderately better than those fired at 300yds. Is there any truth to the statement that long pointy bullets "go to sleep" at some extended range.
 
Are rebated boat tail bullets still sold? My guess is that there is no advantage to them as obduration is not a factor


Posted By: Stevey
Date Posted: October/02/2010 at 00:26
SmileOn the obduration question -- at say 50,000 to 65,000 psi anything that can be deformed or squashed will be obdurated and accelerated (progressive gun powders). Acceleration is a result of a force rather than causing a force.


Posted By: helo18
Date Posted: January/16/2011 at 17:19
Thanks for the bump Wes. I was looking for that chart recently.

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To be prepared for War is one of the most effectual means of preserving peace.

GEORGE WASHINGTON


Posted By: budperm
Date Posted: January/17/2011 at 09:42
Can a moderator Please Pin this post! Bandito

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"Peace is that brief glorious moment in history when everybody stands around reloading".
--Thomas Jefferson





Posted By: Bigdaddy0381
Date Posted: March/17/2011 at 06:31
this is the thread I was looking for.

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P&Z Firearms , Pro gun cleanings and gun repair and wood refinishing.

Ecclesiastes 10:2


Posted By: budperm
Date Posted: March/17/2011 at 06:35
Yepper, its definitely one of the better ones!!!
 
Good help to us all not just newbies!


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"Peace is that brief glorious moment in history when everybody stands around reloading".
--Thomas Jefferson





Posted By: xiaochun3612
Date Posted: May/31/2011 at 23:57
I would try both to see which provided better accuracy, if they are equal then get teh 175. It will fight the wind better than the lighter grain.  With a 10 twist you may even be able to put some bullets up to 200gr or even the 208 hornady a max.  I know this doesn't really answer.

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Believe myself.
\


Posted By: snakeman48
Date Posted: December/30/2011 at 20:20

Finally found this chart, again

Been lookin' for it, found it, then lost it.

Thanks


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NRA Benefactor Member.    Veteran; US Army 5th Corps 1970-1972

The only time in my life when I got to Rock-N-Roll, and the ammo was free!!


Posted By: River Runner
Date Posted: May/10/2012 at 05:18

So if I know the twist rate of the barrel on my gun, should I choose a bullet weight based on that twist?  And is the twist rate easy to find out?  I have a Winchester model 88 in .308.



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Randy


Posted By: 3_tens
Date Posted: May/10/2012 at 09:11
Each barrel has different dynamics. Even 2 barrels that are made by the same machine one right after the other will shoot different. Learning your weapon comes from careful notes maintained over time. Then about the time you get it all figured out its time to re-barrel the rifle and start all over again. Wink


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Folks ain't got a sense of humor no more. They don't laugh they just get sore.

Need to follow the rules. Just hard to determine which set of rules to follow
Now the rules have changed again.


Posted By: Stevey Ducks
Date Posted: July/20/2012 at 01:52
1 - 11 twist for .308 diameter bullets 190 gr or more?
 
1-14 gr. for the real fast stubby ones.


Posted By: 338LAPUASLAP
Date Posted: October/27/2012 at 17:17
GOOD Thread BUMP even though it is a sticky icky...

I have found limits as far as speed and weight that are factors as well as barrel material and heat of barrel and specific heat properties a factor as well as bullet material hardness and coef rise.

BUMPED

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No one


Posted By: nralifer
Date Posted: August/15/2016 at 22:49
I thought I might post something on this thread since there has not been one in a long time.  The subject of stability and barrel twist rate is something that I know a little about since I have had to deal with it a lot.  Stability is a function of bullet length, caliber muzzle velocity, air density and all the factors that influence that, and bullet weight.  The simplest thing to do is to go to the JBM Ballistics site and play with their bullet stability calculator.  To be sure that the bullet one wishes to try will be stabilized by a barrel of a given twist simply measure with a calipers the length of the bullet, weigh it, and plug in the numbers into the JBM calculator. For atmospheric variables one can use standard conditions such as 59 degrees F, 29.92 in Hg, and 50% humidity. For a bullet to be stable under most conditions, a stability factor of at least 1.4, and preferably 1.5 is needed.  As the atmospheric pressure increases and the temperature decreases, the air gets denser and the stability factor decreases. A bullet, when shot in the summer, may appear stable, but come winter time the stability may not be there (hit sideways or shoot bad groups on cold days).  When the stability factor under a given set of conditions falls below 1.25 then weird things can happen like it is accurate at 200 yds but key holes at longer ranges.  Also it will have a tendency to tumble through the target and have erratic penetration through an animal since flesh is denser than air.

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It is hard to fail, but it is worse never to have tried to succeed. TR


Posted By: Peddler
Date Posted: August/16/2016 at 05:15
Welcome to the OT George.

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When you are dead, you don't know you are dead.It is difficult only for others.

It is the same when you are stupid.


Posted By: Bigdaddy0381
Date Posted: August/16/2016 at 06:33


This is my best load to date. I like to use the side of the bullet for a better energy dump. The bullet dose not mushroom out like some I have seen, but they do have good knock down power. To get this fine groups at 200 yards I have to use a slower twist and heaver bullets.s This is 200 yard 5 shot group.



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P&Z Firearms , Pro gun cleanings and gun repair and wood refinishing.

Ecclesiastes 10:2


Posted By: nralifer
Date Posted: August/17/2016 at 05:36
Thank you Peddler.It's a really interesting forum. Enjoyed Bigdaddy's  pic. Looks familiar. Have a great friend who likes to machine his own bullets for this monster 338 Lapua. He made a 325 gr machined copper bullet about as long as the Texas panhandle that actually shot sub minute of angle groups out to 3-400 yds. (not sure which one now). We wanted to test it at a longer range and so we set up a target at 500 yds. It was a a very cold day (5degrees,and pressure was 30.30 in Hg). Shot three shots, and all the holes looked like Bigdaddy's pic. The funny thing was the group was minute of angle!  We actually spoke to a Hornady ballistician about the phenomenon and he said it was not possible. Glad to see that someone else has witnessed the impossible as well.

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It is hard to fail, but it is worse never to have tried to succeed. TR


Posted By: DCAMM94
Date Posted: August/22/2016 at 14:10
I once had groupings like that (consistently) out of my old .243 Encore 15" handgun.  The only thing it would shoot consistently was 85gr, and I had to use compressed loads or the older hornady overcooked loads.  It was a 1-11" I believe.  Now I use a 7-08 barrel with a 1-9 twist, and it will hold a spiral a little better than a Billy Kilmer pass - at least out to 300yds - with up to 140grainers.

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Although personally I am quite content with existing explosives, I feel we must not stand in the path of improvement. -Winston Churchill


Posted By: nralifer
Date Posted: August/25/2016 at 06:35
Since that experience if there is a question about stability we try and test in cold weather and for 500 yds or better.

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It is hard to fail, but it is worse never to have tried to succeed. TR



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