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1 in 9" twist AR's: A thing of the past? Login/Join 
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Picture of TRshootem
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Jelly pointed out that indeed some bullets come apart. Those 50 gr (SX) super explosive in a .22-250 or a Swift seldom make it to the critter when pushed as fast as possible. As to twist, a 16" AR shooting Hornady 75 gr BTHP Match in a 9 twist barrel will most often be plenty accurate out 3-400 yds. Mine seems to love em with a load of Tac. Just how accurate is some twist info really, certainly one could be 8.7 or 9.4 etc.
 
Posts: 1209 | Location: Montana | Registered: October 20, 2007Reply With QuoteReport This Post
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quote:
Originally posted by CD228:

Have you actually observed a bullet tear itself apart? I've read the same anecdotes on line, but I have never seen it happen in real life.


I have seen a bullet come apart. I was spotting for a buddy of mine he has a 1X7" twist 24" barreled match AR 15. He was shooting Berger 90gr. VLD bullets and four of them came apart at the 1000 yard line, just a few yards from the muzzle.

The Berger bullets use J4 jacketing and it is a little softer than most other jackets, we figured that it was the softer jackets, a fairly new barrel and higher velocity that was a contributing factor, and probably not quite up to standards bullets that lead to the failures.

So yes, I have seen it. They looked like a little blue puff. The bullets that didn't come apart were all 9, 10 and X's. Iron sight match.


As for the most useful twist rate in 5.56/.233 I believe it's 1X7.5/1X7.7" or 1X8" twist. They will cover most bullet weights from 50gr. to 80/90gr. VLD bullets.


ARman
 
Posts: 2307 | Registered: May 19, 2010Reply With QuoteReport This Post
Hop head
Picture of lyman
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quote:
Originally posted by fritz:
quote:
Originally posted by lyman:
my short range AR, (service Rifle) will put 69gr SMK's inside an inch at 100,

Every barrel I have owned shoots quality 69 SMK loads well. Twists of 1/9 through 1/7, barrel lengths of 14.5" through 24". Chambers of 5.56, 2.23, and Wylde. I think it's just a great bullet design, and I suspect it's pretty tolerant of jump/jam to the lands. For some of my barrels, 69 SMK loads produced the tightest groups of all loads at 100 yards -- bugholes which appear to have been shot by bolt actions. It's unfortunate that the 69's G1 BC is so low at .301.

The match bullets in the 73-77 grain class offer noticeably superior GI BCs of around .400, but they can be finicky in some barrels. Especially those with 1/9 or slower twists. Hornady's 75 BTHP and Sierra's 77 MK are widely used with good results. Hornady's 73 ELD-M seems to like tight chambers and/or limited jump.

For lighter bullets, Hornady's 55 Vmax tends to be accurate in barrels without regard to twist rates. Its G1 BC of .255 is unspectacular.



neither of mine will shoot a 75, nor do they like 68gr Noslers,

55's, ok, (just tried standard M193 type bullets,)

they also do very well with 52SMK's



www.chesterfieldarmament.com
 
Posts: 7903 | Location: Beach VA,not VA Beach | Registered: July 17, 2007Reply With QuoteReport This Post
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Every barrel is different. Black Hills 52 SMK is accurate in all my uppers. Haven't shot any 68 Nosler.

I'm in the process of breaking in an 18" Bartlein/Craddock 1/7.7 barrel, Wylde chamber. Maybe close to 200 rounds to date, probably close to 100 today. So far it's showing a preference for Federal GMM 69 and Hornady 75 HPBT. Decent, but a little inconsistent results with ADI 69 SMK. This may be my first barrel that doesn't shine with Hornady VMax 55. First time with Hornady 73 ELD was good, today not so much.

Today's 100-yard groups were .66" and .91" with Hornady 75 -- .75" and 1.06" with FGMM 69.

Shot the Hornady 75s at six plates from 340 to 693 yards. Looks like the barrel is speeding up a bit. Once I adjusted dope for a little less elevation, dinging the targets was pretty easy. Looks like this is my competition round, with FGMM 69 as a backup.
 
Posts: 6215 | Location: Colorado | Registered: January 26, 2008Reply With QuoteReport This Post
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quote:
Originally posted by ksss:
The faster the twist the more stable the bullet as the yaw is kept tight during flight. The 1/7 twist of the M-16A2 and everything since didn't need the fast twist to stabilize the 55 grain bullet that was common until the M855/SS109 which is 62 gn. We were issued this in the mid 80's. Tt was fast to stabilize the tracer rounds which I believe were about 69 gn if I remember correctly. The A1 had a much slower twist at 1/14. This is why the A1 was considered so deadly if you were hit with the 55 gn round fired from this rifle. The yaw was much more loose, and went unstable when it hit anything, including the human body causing significantly more trauma than say a 55 gn FMJ fired from a 1/7 twist. As heavier bullets become the norm, the fast rate is needed to keep the yaw tight which allows for greater accuracy.


The A1 is a 1/12 twist.

1/9 barrels work fine for general use with the 55 and 62 grain bullets.

For heavier bullets like 69, 70, 75 and 77 grain 1/7 and 1/8 are the way to go.
 
Posts: 408 | Location: Texas | Registered: March 25, 2013Reply With QuoteReport This Post
Wait, what?
Picture of gearhounds
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Have you actually observed a bullet tear itself apart? I've read the same anecdotes on line, but I have never seen it happen in real life.

I have personally seen lightweight .223 varmint bullets leave visible trails through the air out of 1/7 barrels. While none of them blew apart in midair, they were certainly shedding material.




"Live every day as if it's going to be your last, and one day, you'll be right.”
Malachy McCourt
 
Posts: 11040 | Location: Martinsburg WV | Registered: April 02, 2011Reply With QuoteReport This Post
Freethinker
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quote:
Originally posted by gearhounds:
they were certainly shedding material.


I have never noticed that with rifle bullets, but it has obviously occurred with some handgun bullets I’ve seen fired.







“Most men … can seldom accept the simplest and most obvious truth if it … would oblige them to admit the falsity of conclusions … which they have woven, thread by thread, into the fabrics of their lives.”
— Leo Tolstoy
 
Posts: 40474 | Location: 10,150 Feet Above Sea Level in Colorado | Registered: April 04, 2002Reply With QuoteReport This Post
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quote:
Originally posted by ARman:
quote:
Originally posted by CD228:

Have you actually observed a bullet tear itself apart? I've read the same anecdotes on line, but I have never seen it happen in real life.


I have seen a bullet come apart. I was spotting for a buddy of mine he has a 1X7" twist 24" barreled match AR 15. He was shooting Berger 90gr. VLD bullets and four of them came apart at the 1000 yard line, just a few yards from the muzzle.

The Berger bullets use J4 jacketing and it is a little softer than most other jackets, we figured that it was the softer jackets, a fairly new barrel and higher velocity that was a contributing factor, and probably not quite up to standards bullets that lead to the failures.

So yes, I have seen it. They looked like a little blue puff. The bullets that didn't come apart were all 9, 10 and X's. Iron sight match.


As for the most useful twist rate in 5.56/.233 I believe it's 1X7.5/1X7.7" or 1X8" twist. They will cover most bullet weights from 50gr. to 80/90gr. VLD bullets.


ARman


I'm going to correct a few things and then present another possibility for what you saw.

First off, the J4 jackets are made by Berger. They supply these jackets to a great many bullet makers, one of them being the erstwhile JLK outfit where I used to get my match bullets. I believe Sierra makes their jackets and I know Hornady does. I suspect there are other makers but the J4 has long been considered the gold standard in jackets.

There are two types of jackets; those for hunting bullets and those for match bullets. The hunting bullet jackets are thinner than the match jackets. The match jackets are mean to stay together and be abused in velocities, spin rate and so on.

I know a number of people who shoot the 90gr Berger VLD in competition and their twist rates range from 1:6.5 to 1:7. Some use them in bolt action rifles with long barrels like 26 or 28 inches and proper that bullet at much higher velocities than you can expect from an AR-15. They have never reported any breakups.

What a lot of people forget is that the twist rate is one of two factors that create the spin on the bullet. The other factor is velocity. If your bullet exists the muzzle at 3000 FPS and the twist rate is 1:12; the spin rate is calculated as follows: 3000 X (12/12) X 60 = 180,000RPM. A quicker version is MV X (720/12) = 180.000. So let's take you 90 gr bullet out of an AR with a 1:7 twist. I figure the MV will be about 2500FPS for the 90gr in a short 24 inch barrel. I shot many thousands of 80gr JLKs with the same J4 jacket out of a 26 inch barrel at 2650FPS and I had to take several steps to mitigate the pressure. So, your 2500 X (720/7)= 257,142 RPM. My 2650 X (720/7.7)= 247,792RPM. Very small difference. But let's go further. Let's take a 77gr bullet pushed out at 2750 pushed in a 1:7: 2750 * (720/7) = 282,857 RPM. Hmm, I've never heard of a 77 gr bullet coming apart out of an AR and yet the RPM is quite a bit higher. What does a 55gr do at 3200FPS: 3200 * (720/7) = 329,142RPM. Wow, and yet' I've not heard of 55 gr bullets 'splodin' out of an AR. Now a 40 gr at 3400: 349,714RPM. The mind boggles with that number and yet that doesn't seem to happen either. And we know the jackets for these varmint bullets is VERY thin.

So why did you see some 90gr bullets explode coming out at pretty sedate velocities? The answer may lie in one thing you said: The barrel was new. How new is "fairly new"? Is is also possible that there were tool marks left from say the chambering that may have damaged the jacket during the firing? That's usually the culprit; a damaged jacket comes apart in flight.

The bottom line is your explanation does not hold water, you dismissed the issue too quickly without any facts.
 
Posts: 3011 | Location: Texas | Registered: June 20, 2012Reply With QuoteReport This Post
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Originally posted by gearhounds:
quote:
Have you actually observed a bullet tear itself apart? I've read the same anecdotes on line, but I have never seen it happen in real life.

I have personally seen lightweight .223 varmint bullets leave visible trails through the air out of 1/7 barrels. While none of them blew apart in midair, they were certainly shedding material.


What do you mean by "visible trails?" Can you describe them? Are you sure you didn't mistake the "visible trail" for a "vapor trail?" In my countless years of competition, as a shooter, a wind coach or a teacher, I have seen endless vapor trails or what we call the "trace" of a bullet in flight. We have used that to see when the shooter was going and to be able to get the shooter on target. I have even captured video of such things, that I use to teach long range shooters. One of the posters here, fritz, mentions being able to see the trace very often and that helps him call his own shots.

If a bullet was damaged and was "shedding material" that you could actually see in flight, that bullet would be disintegrating at worse, or very off course at best.
 
Posts: 3011 | Location: Texas | Registered: June 20, 2012Reply With QuoteReport This Post
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Originally posted by sigfreund:
quote:
Originally posted by gearhounds:
they were certainly shedding material.


I have never noticed that with rifle bullets, but it has obviously occurred with some handgun bullets I’ve seen fired.





We need a LOT MORE data. What kind of bullets? What distance? Whose ammo? What caliber? What handgun? etc.

The patterns you show indicate some type of powder leakage from 2 grooves.
 
Posts: 3011 | Location: Texas | Registered: June 20, 2012Reply With QuoteReport This Post
Freethinker
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I must agree with NikonUser about the “trails” seen with rifle bullets. Although I didn’t elaborate about the pictures I posted above, visible loss of lead from the base of the bullet can obviously occur only if the base isn’t covered, as in bullets with fully-covered noses used in M193 or M855 ammunition (for example). Except for something like a Nosler partition bullet, virtually all bullets intended for hunting, match shooting, etc., have bases that are covered by jacket material.




“Most men … can seldom accept the simplest and most obvious truth if it … would oblige them to admit the falsity of conclusions … which they have woven, thread by thread, into the fabrics of their lives.”
— Leo Tolstoy
 
Posts: 40474 | Location: 10,150 Feet Above Sea Level in Colorado | Registered: April 04, 2002Reply With QuoteReport This Post
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quote:
Originally posted by NikonUser:
We need a LOT MORE data. What kind of bullets? What distance? Whose ammo? What caliber? What handgun? etc.

The patterns you show indicate some type of powder leakage from 2 grooves.


Unburned powder caused the small dents in the paper in the second photo, but not the gray spray pattern. There are even a couple of grains embedded in the paper at the lower right of the photo. If powder leakage were the cause, the pattern could not be an ever-tightening spiral. The powder would disperse, but it wouldn’t form such a well-defined pattern. In fact, only a continuous source that is spinning as it approaches the paper would be capable of producing such spiral patterns. Also, as can be seen by the small tear in the paper close to the lower bullet hole, the impact force of the leaking lead increases as the bullet gets closer.

As indicated by the unburned powder particles visible in the lower photo, the shots were fired from very close range; as I recall they were fired from the “close combat” position not much more than arm’s length from the targets. Shots fired from greater distances did not produce the patterns on the targets.

Ammunition was commercial reloads, 9mm Luger, and probably 115 grain FMJ. Pistol was, I believe, an S&W M&P.

Another:





“Most men … can seldom accept the simplest and most obvious truth if it … would oblige them to admit the falsity of conclusions … which they have woven, thread by thread, into the fabrics of their lives.”
— Leo Tolstoy
 
Posts: 40474 | Location: 10,150 Feet Above Sea Level in Colorado | Registered: April 04, 2002Reply With QuoteReport This Post
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Interesting.
I have a 6.5 twist AR because that is what it says on the label of the 90 gr Sierra.
The 90 gr SMK shoots fine up to the maximum Sierra load but that is not enough to stay supersonic at 1000 yards. Overloaded to stay supersonic, they don't all make it to the target. I finally caught a couple on a 100 yard target; the bullets were BENT and left a C shaped hole in target and backer.

JLK and Berger 90 gr would handle the heavy loads and shoot well at 1000.

I tried a box of 75 gr Amax. Loaded hot they broke up, my spotter could see the fragments twinkling in the sunlight. When they hit they were accurate, I had a target that was nothing but tens, Xs, and misses due to failed bullets.

Loaded down to what the bullets will stand, all are accurate, it is a great 600 yard rifle, but not the equal of the .308 at 800-1000 no matter what the BC indicates.
 
Posts: 2800 | Location: Florence, Alabama, USA | Registered: July 05, 2001Reply With QuoteReport This Post
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I used the 75 A-Max in the early part of my F-TR career to get to 1000 yards. I had a problem keeping then supersonic at 1000 yards and then I read that the tip would melt or deform and do strange things during the long trip to the target; a deformed nose will cause the bullet to deflect by inducing a dynamic instability in the bullet. Think of it as a badly thrown football.

So, I stopped with the A-Max and went to the 80grainers and never looked back.
 
Posts: 3011 | Location: Texas | Registered: June 20, 2012Reply With QuoteReport This Post
fugitive from reality
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Another issue with the 1/9 twist rate is not all 1/9 barrels are created equal. ARFCOM used to be alight with reports of people measuring their twist rate, and coming up short in regards to the 1/9. This seemed to be a problem with the lower tier lower quality barrels, and you'd never know if all you shot was the lowest price M193/M855 type ammo.


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Posts: 6385 | Location: Newyorkistan | Registered: March 28, 2007Reply With QuoteReport This Post
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Originally posted by SgtGold:
Another issue with the 1/9 twist rate is not all 1/9 barrels are created equal. ARFCOM used to be alight with reports of people measuring their twist rate, and coming up short in regards to the 1/9. This seemed to be a problem with the lower tier lower quality barrels, and you'd never know if all you shot was the lowest price M193/M855 type ammo.



when I was a regular shooter in the Service Rifle world, I recall some of the HM's and State Team guys were double checking twist on new barrels,

someone had bought one that was supposed to be 1:7.7 but was more like 1:7.5 or similar,,

after much hand wringing and consternation, all was good since the rifle shot well



www.chesterfieldarmament.com
 
Posts: 7903 | Location: Beach VA,not VA Beach | Registered: July 17, 2007Reply With QuoteReport This Post
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1/9 is ideal for 55-62 grain. I wish it were more popular, but it practically died ten years ago with the infamous AR15 chart.


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Posts: 5478 | Location: Floriduh | Registered: October 16, 2004Reply With QuoteReport This Post
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Originally posted by bubbatime:
1/9 is ideal for 55-62 grain. I wish it were more popular, but it practically died ten years ago with the infamous AR15 chart.

I've shot out virtually identical Wilson Combat 1/7 and 1/9 barrels, and I'm well into the useful lives of two Wilson Combat 1/8 barrels. All four have shot 55 and 62 grain FMJ loads with essentially identical results. All four have shot 40, 55, and 60 grain VMax loads with essentially identical results.

In my experience, both 1/8 and 1/7 twist barrels are ideal with 55-62 grain loads. I'm not the only one with such experience, hence a good reason for the demise of 1/9 barrels. 1/9 barrels are still out there, and they are often on sale during holidays.
 
Posts: 6215 | Location: Colorado | Registered: January 26, 2008Reply With QuoteReport This Post
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Picture of highlander81
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Originally posted by CD228:
quote:
Originally posted by RogueJSK:
quote:
Originally posted by sigfreund:
No matter how carefully manufactured, all bullets are imperfect. The variations are usually very tiny, but they nevertheless exist, and poorer quality bullets are more imperfect. The relationship between bullet imperfection and rifling twist rate is that the faster the bullet spins, the greater effect the imperfections have on precision. That’s why precision benchrest shooters at close ranges (e.g., 100 yards) prefer slower rifling twists.


In addition, some lightweight, especially thin-walled varmint bullets can tear themselves apart if fired through a barrel with too tight of a twist.

So there are a few situations in which a slower twist rates would be preferable.


Have you actually observed a bullet tear itself apart? I've read the same anecdotes on line, but I have never seen it happen in real life.


Going back decades, my first AR was an SP-1 with a 1/12 twist barrel. Back then I settled on a great handload that shot well: 2x.x grains of Winchester 748 with a Speer 52 grain Hollow point. A light jacketed varmint Bullet. Had a ton of fun using that rifle on gophers when it was still legal up here to do that with an AR.

Then I purchased my first 1/7 twist barreled AR, a match HBAR. Took that to the range and naturally took my proven handload with the 52 grain Speer HP bullets.

Fired my first 5 rounds at 100 yards and not a mark on the paper. (I had bore sighted the rifle in case someone wants to get after me for the distance).

Then my buddy noted that there were round strikes all over the place when I fired within a few yards left and right of the target.

Next attempt at getting on paper we noticed a light coloured puff in the air between 50 and 75 yards from the muzzle each shot. I switched to 55 grain Winchester white box and the problem ceased. I assumed at the time that the bullets were disintegrating and haven’t used that load since changing the SP-1 barrel to a 1/7 twist.
 
Posts: 434 | Location: Southern Alberta, Canada | Registered: April 17, 2008Reply With QuoteReport This Post
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