.223 Twist Rate?

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2ndtimer

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My experience with .223 Rem bullets and twist rates has always been with 1 in 12" twist bolt guns (26" Remington and 22" Weatherby Vanguard) and 1 in 8" AR's (24" Stag and 16" S&W original Sport with 5R barrel). I shot a lot of 40 gr through 55 gr bullets through the bolt guns without issue. They seemed to prefer the 40 and 50 gr bullets. The 1 in 8" AR's got more of the 55 gr bullets and some heavier bullets as well. I avoided the really thin jacketed bullets in the AR's (Hornady SX, Speer TNT) for fear of bullet destruction due to fast twist rate. Surprisingly, the 40 gr tipped bullets (Nosler Ballistic Tips, Hornady V-MAX and Z-MAX) shoot very well out of the AR's. I also avoided the heavier bullets in the 1 in 12" bolt guns, assuming the 69 gr bullets would be unstable and be tumbling at the target. At the range yesterday, I decided to try one of my 69 gr Nosler loads in the 26" 1 in 12" Remington just to see how inaccurate they would be. To my surprise, 5 shots at 100 yards grouped in less than .75 of an inch! Could this be attributed to the higher velocity provided by the 26" barrel allowing the longer bullet to stabilize? Any thoughts? That Remington 700 SPS Varmint shoots everything well, but I have never tried a bullet weighing more than 55 gr before, since "everyone knows you need at least a 1 in 9 twist for a 69 gr bullet in a .223".
 
My .223 Remington and 5.56 NATO experience runs as follows. My bolt gun is a custom 1:12 I built years ago. The rifle shoots 55 grain and lighter bullets extremely well. Regardless of bullet length or shape 55 grains is as good as it gets with the 1:12 bolt gun. I have a few semi-auto guns also. A pair of Colt SP1 rifles I have are also 1:12 and like the bolt gun I never had much luck with any bullet over 55 grains. I have a Colt Target Sporter with a 1:7 twist as well as a custom AR with a 24" match barrel and I like both of these rifles as both shoot the heavier bullets, including the 80 grain Sierra MK extremely well but the 80 grain MK bullets need to loaded one at a time due to their length. While everyone claims they do fine using 55 grain bullets in a 1:7 twist my accuracy has never been anything great using the lighter and shorter bullets in the faster twist barrels.

Ron
 
If you know the muzzle velocity out of the 26" barrel then the rotation can be calculated to see if it is spinning at a rate that is stabilizing the bullet.
 
I will try to chronograph the 69 gr loads out of the 1 in 12 twist barrel and see how fast the are exiting the barrel. I was just surprised that they grouped decently and made round holes in the target.
 
Twist rate, bullet geometry, velocity, air density and temperature are all factors. Try playing with JBM's stability calculator:

http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi
http://www.bergerbullets.com/twist-rate-calculator/


For short range, a bullet is either stable or not, the Miller stability factor won't matter much.

Long range, a factor of 1.5-2.5 is ideal. The BC will be reduced with a factor less than 1.5, and it's possible for an extremely high stability factor to produce extra drag through precession, and yaw of repose causing more spin drift and drag.

http://bulletin.accurateshooter.com...fficent-varies-with-twist-rate-stabilization/
http://bulletin.accurateshooter.com...on-of-bullets-why-is-too-much-spin-a-problem/
https://thearmsguide.com/5346/long-range-shooting-external-ballistics-spin-drift-13-theory-section/
 
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The extra muzzle velocity definitely helps. I never tried anything heavier than 60gr VMax or 64 gr WW PP (but that is a short fat bullet) in my Remington VS, may just give the 69 Sierra a try!
 
I've found three "heavy" bullets that shoot extremely well in my Sako rifles, which have a 1 in 12 twist: Sierra 65 gr Game King, Winchester 64 gr Power Point and Speer 70 gr soft point. I've gotten 1/2 MOA 5 shot groups with the Sierra bullets. I'm using H335 and 748 powder.
 
Since stability improves with velocity, lower bullet length, and less dense air, it would be good for all involved to share bullet lengths, velocity if you know it, and what altitude and temperatures you are shooting in.
 
Good points.

My shooting was done at approx 5,000 ft elevation and temperatures ranged from 70 to 80 degrees.

65 gr Sierra – H335 powder– 2.245 OAL – Est Velocity 3025

70 gr Speer – H335 powder – 2.220 OAL – Est velocity 2765

I don’t have the load information for the 64 gr Power Points handy right now but I can dig it up later if anyone really needs it.

Note: the 70 gr Speer has to be seated deep to avoid contact with the rifling.

I apologize for the estimated velocities but it has been too windy to set up my chronograph. I can normally estimate within 50-75 fps though. If we ever get a break to these spring winds, I'll take the chronograph out and post the exact readings.
 
I've pretty much found exactly the same thing as in the first post,
Slower twist rate, lighter bullet, reasonable muzzle velocity equals inherent accuracy.
Faster twist rates, higher velocity needs a longer/heavier bullet.
My 1:8 & 1:9 barrels like 65 and up bullets,
The mid twist rates like medium weight,
The 1:14-1:16 like the super light bullets.

As a historical note, manufacturers did exactly the same thing.
As bullets got longer, heavier & faster, twist rates increased.
The military push for heavier bullets had a lot to do with that once the AR platform was adopted, the military having billions of dollars to do research with figured it out pretty quickly...

All I can say is, I'm REALLY GLAD there are so many choices in the .223/5.56 platform! Makes that little, low recoil round much more useful for a lot more things.
 
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