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Functional
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Posted: 11/7/2010 12:53:06 AM
[Last Edit: 11/7/2010 12:54:58 AM by Functional]
This has been discussed before here on AR15.com and other AR15 forums. Which is better the nato 1:7 compared to a 1:9 nato (or advertised as nato). Nato milspec is firing a nato spec round ie M855 SS109 Penetrator, 62 grain (ex. Lake City). The 62 grain bullet will stabilized better/quicker than the 55 grain bullet ie XM193 which is also a milspec bullet. The 1:9 does accommodate a wider range 55 - 75 grain bullet better than the 1:7. The 55 grain is probably more readilly (price) available for a regular shooter. Most of you are shooting with barrel that have the 1:7 twist. My RRA barrel has been replaced by a nato mil spec 1:9 twist M1S Chrome line chamber & bore barrel. What's your take on this!!
luceri
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Posted: 11/10/2010 1:23:21 PM
1:7 –– barrel length doesn't matter in my experience for twist so with the pistol, why not go 1:7 and get the most accurate round you can? I know it's arguable, but that's my experience.
FALPhil
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Posted: 11/10/2010 2:10:35 PM
[Last Edit: 11/10/2010 2:16:57 PM by FALPhil]
Originally Posted By luceri:
1:7 –– barrel length doesn't matter in my experience for twist so with the pistol, why not go 1:7 and get the most accurate round you can? I know it's arguable, but that's my experience.

Very arguable. There is a reason varmint hunters use slower twists for their lighter bullets, and it has everything to do with accuracy. The proper answer would have been, "It depends on the bullet weight you intend to use most of the time".

My take is that if you are going to use the lighter weights, use the slower twist. For heavier weights use the faster twist. Since these are pistol length barrels, it makes more sense to use heavier bullets if you are going to do anything other than paper punching. Therefore, unless your pistol is just a range toy, go with the faster twist for heavier bullets. That's my opinion.

Now, if excellent accuracy is your primary concern, there are a lot more variables to consider. For instance, you typically don't get great accuracy with a chrome lined barrel. In .224 diameter bullets, the lightweight varmint bullets tend to be very accurate, so you would want the slower twist.

Use the right tool for the job.

Tire
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Posted: 11/10/2010 3:52:39 PM
Well about that right tool for the job... you realize that that 1:9 twist stand for 1 complete revolution in 9 inches right? though we should match our bullet weight to our twist in a conventional RIFLE barrel that might be 16-26 or more inches therefore giving the bullet multiple revolutions I dont think that would apply so much in a barrel that is say 7.5"s in fact if you look at conventional handgun twists they are much much SLOWER! look at a 1911 typical rate is 1:16 oh surely they must be throwing the lightest of bullets When dealing with pistol lenght barrels you need to figure in the speed and lenght of what you are shooting too. the common twist for a 22LR is 1:16 ... needing faster twist for bullets approaching 60 grains... but still nowhere near 1:7 or 1:9..
FIGJAM
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Posted: 11/10/2010 4:35:06 PM
[Last Edit: 11/10/2010 4:39:01 PM by FIGJAM]
Barrel length (aside from the obvious relationship with velocity) is not a factor in the equations for determining optimal twist.

http://kwk.us/twist.html

http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi
Functional
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Posted: 11/10/2010 11:45:33 PM
Originally Posted By Functional:
This has been discussed before here on AR15.com and other AR15 forums. Which is better the nato 1:7 compared to a 1:9 nato (or advertised as nato). Nato milspec is firing a nato spec round ie M855 SS109 Penetrator, 62 grain (ex. Lake City). The 62 grain bullet will stabilized better/quicker than the 55 grain bullet ie XM193 which is also a milspec bullet. The 1:9 does accommodate a wider range 55 - 75 grain bullet better than the 1:7. The 55 grain is probably more readilly (price) available for a regular shooter. Most of you are shooting with barrel that have the 1:7 twist. My RRA barrel has been replaced by a nato mil spec 1:9 twist M1S Chrome line chamber & bore barrel. What's your take on this!!


62gr bullet stabilizes better than the 55gr (most pistol shooter use). I am shooting 62gr for Plinking & Personal Defense. 1:9 in the 11.5" barrel stabilizes the 62gr bullet very well. I think 1:9 is better/more accurate for Pistol with shorter distances. If you are shooting long distances you should be shooting out of a 16" or 20" barrel. Pistols are very close quarter-quick acquistion guns.
iNeXile556
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Posted: 11/13/2010 11:06:44 PM
It is projectile length, not weight, that determines optimal twist rate.

If you have an 11.5" 5.56 barrel I'd go for a 1:7 myself. The 77gr rounds are very nice out of my 10.5. It also has no problems at all with 55gr. Truth be told I shoot the Federal T223D (40gr Sierra HP) out of my 1:7 and it does just fine.



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