The best combo for killing, is 1/9 twist sending a 55gr.

7 twist works, but too fast and pin cushions upon impact creating more pass thru shots.

I’ve found that even with m193, and shooting a 1/9 or slower, you get more yaw effect which creates a larger temporary wound channel, more shock, and more blood loss.

M193 fails to fragment below 2600 FPS but often fragments above that threshold. This isn't influenced by twist rate. If you have some evidence demonstrating otherwise, please share. I've heard repeated claims about better terminal performance with slower twists but I've never seen anything to back them up.

Even when it does fragment, M193 doesn't perform nearly as well as a wide variety of newer loads.

Proof?
A theoretical difference doesn't mean than there is a noticable practical difference

“Fragment”
Is fragmenting supposed to be a superior trait?

When a projectile breaks apart it loses energy, velocity, and penetration. I’m assuming you just repeated what you heard somewhere and this is not your personal field knowledge.

I’ve been involved in over 9500 wild boar deaths and many other coyote kills.

Most all with 5.56mm.

Those fragmenting bullets you seem to like, suck.

Oh look.  The piggy killer who thinks that he can detect "significant spin drift" at a few hundred yards shooting M193 from an AR-15,  is back with his ignorant BS again.

If anyone wants a good laugh, read this whole thread from the beginning . . .

https://www.ar15.com/forums/AR-15/PSA-5-56-nato-1-7-shooting-223-best-coyote-rounds/16-777460/?page=1#i8500689

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It's definitely my preferred, though I also find variability in 1/7 bbl types with how well they shoot the same ammo.

The purpose is to hit what you aim and at and it stops shooting back or dies if it is a varmint.  193/855 is the most common ammo out there.  Learn to shoot it. Because when all the fancy round makers are told to produce for the military they will produce 193/855, and your 72/77 gr ammo will dry up fast.  And you will not have trained with the ammo you can get.

2 way ranges change everything.

You're telling me M193 doesn't fragment?

All expanding and fragmenting bullets "lose energy" when they expand or fragment. You seem to think that M193 doesn't frag, but rather that it only yaws like the Russian military 5.45x39 rounds. You also seem to think that this yaw characteristic only occurs with slow twist barrels. None of this is true.

M193 can fragment, though not entirely reliably, above 2600 FPS. This has nothing to do with twist rate. When it fails to frag, it does act much like a 5.45 7N6 or 7N10, but again, this behavior does not change based on twist rate. Most non-expanding, non-fragmenting bullets will yaw, but this doesn't create nearly as much damage. M193 does penetrate sufficiently against a human or human-sized animal when it fragments, and the newer loads I mentioned do even better.

I'm not sure why you complained about excessive penetration leading to smaller wounds before, but are now acting like a non-deforming bullet offers the best performance because it doesn't lose penetration.

You get to choose the ammo in your stash before SHTF. You could choose good ammo instead of outdated stuff. You could always have recorded zeroes for those outdated types in case you need to use them, but there's no need to procure them to the exclusion of better rounds.

People are choosing the slower twist rates based on misinformation.

This.

Done a lot of comparisons between 1/7 and 1/9 with M193 have you?

Well… That’s a fun read.

55 Grain FMJ Ammunition Fired From AR-15s With 1:9” and 1:7” Twist Barrels


Internet Commandos: "55 grain FMJ bullets are unstable/overstabilized/inaccurate/less-lethal when fired from an AR-15 with a 1:7” twist barrel."

Statements such as the one above always seem to be proclaimed by Internet Commandos, without posting any valid, statistically significant data to support that these effects occur, or that if they do occur, that they do so to any degree that has any significant effect on the accuracy/precision spectrum involved with AR-15s firing M193-type ammunition out to distances of 100 yards.

By definition, an “unstable” bullet will have a gyroscopic stability factor of less than 1.0 at the muzzle.  A typical 55 grain FMJ bullet loaded in M193-type ammunition will have a gyroscopic stability factor of approximately 4.27 when fired from a 20” barrel with a 1:7” twist.

[CaptainObvious] 4.27 is not less than 1.0. [/CaptainObvious]


The following demonstration compares the results of firing four, 10-shot groups of the same lot of 55 grain Prvi Partizan M193 ammunition from two different AR-15 barrels; one barrel with a 1:9” twist, the other barrel with a 1:7” twist.  When chronographed from a 20” Colt M16A2 barrel, the muzzle velocity of this lot of PPU M193 was 3219 FPS with a standard deviation of 35 FPS.

The accuracy specification for M193 cited in MIL-C-9963F is as follows:
The average of the mean radii of all targets of the sample cartridges, fired at 200 yards, shall not exceed 2.0 inches.
These averages are from 10-shot groups fired from machine rested, bolt-actioned test barrels.  All things being equal (which of course they seldom are) this specification equates to a mean radius of 1 inch at 100 yards.









The first barrel used in testing was a 16” Colt HBAR with chrome-lining, a NATO chamber and a 1:9” twist.  This is the barrel found on the Colt 6721.  All of my free-floated Colt 6721 barrels have turned in sub-MOA 10-shot groups at 100 yards when using match-grade hand-loads.

The second barrel used in testing was a 20” Colt HBAR, also with chrome-lining, a NATO chamber and of course a 1:7” twist.  I've owned three of these barrels and they have all turned in 10-shot groups at 100 yards that hover just above one MOA when free-floated and shooting match grade handloads.  I purposely selected the shorter barrel with a 1:9" twist and the longer barrel with the 1:7" twist in order to exacerbate any possible statistically significant influence that the differing twist rates and intendent muzzle velocities might have on the precision of M193-type ammunition when fired at a distance of 100 yards.


Colt 16” HBAR




Colt 20” HBAR






Accuracy (technically, precision) testing was conducted from a distance of 100 yards following my usual protocol. The barrels were free-floated during testing.  The fore-ends of the weapons rested in a Sinclair Windage Benchrest and the butt-stock rode in a Protektor rear-bag. Sighting was accomplished via a Leupold VARI-X III set at 25X magnification and adjusted to be parallax-free at 100 yards. A mirage shade was used. The wind conditions on the range were continuously monitored using a Wind Probe. The set-up was very similar to that pictured below.





The Wind Probe . . .




Four 10-shot groups of the PPU M193 were fired from the 1:9” twist barrel. Those groups were over-layed on each other using RSI Shooting Lab to form a 40-shot composite group. The mean radius of that composite group was 1.08”.
As with the 1:9” twist, four 10-shot groups were fired from the 1:7” twist barrel.  Those groups were also over-layed on each other to form a 40-shot composite group; the results were nearly identical to those obtained from the 1:9” twist barrel.  The  composite group had a mean radius of 1.01”. The two composite groups are shown side by side for comparison.






The entire test as described above was also conducted using a second 16" chrome-lined, NATO chambered Colt HBAR with a 1:9" twist and a second 20" chrome-lined, NATO chambered Colt HBAR with a 1:7" twist.  The ammunition used in this test was all from the same lot of Wolf 55 grain FMJ "Performance Ammunition."  

As before, four 10-shot groups fired from each barrel at 100 yards were over-layed on each other using RSI Shooting Lab and just as before, the mean radii for these 40-shot composite groups showed no statistically significant difference.







Quality, modern lightweight bullets of copper-jacket/lead-core construction can shoot superbly from AR-15s with fast twist barrels. Typical 55 grain FMJ bullets found in M193-type ammunition do not fall into the quality category.

The 10-shot group pictured below was fired at a distance of 100 yards using 55 grain Sierra BlitzKings from one of my Krieger barreled AR-15s.  The barrel has a 1:7.7” twist.  The group has an extreme spread of 0.464".









……

From Dr. G.K. Roberts . . .

"The U.S. Army Wound Ballistic Research Laboratory conducted terminal performance testing using 5.56 mm 55 gr M193 FMJ ammunition fired in 20” barrels of 1/14, 1/12, 1/9, and 1/7 twist rates. [span style='color: red;']No difference in terminal performance was noted between shots made with the different twists. Similar testing was conducted with 5.56 mm 62 gr M855 FMJ ammunition fired in 1/9 and 1/7 twist barrels. [span style='color: red;']Again, no difference in terminal performance was noted."

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An Accuracy Comparison of M855 When Fired From AR-15s With 1:9” Twist and 1:7” Twist Barrels.







This test will compare the accuracy (technically, precision) of IMI M855 at a distance of 100 yards, when fired from an AR-15 with a chrome-lined, NATO chambered barrel with a 1:9” twist and an AR-15 with a chrome-lined, NATO chambered barrel with a 1:7” twist.  The IMI M855 is one of the most accurate and consistent loadings of all the M855 clones that I have tested.

IMI M855 is loaded with a 62 grain FMJ bullet with a cannelure. It also has a steel penetrator seated in the ogive portion of the projectile. This makes the projectile unusually long for its weight, as well as giving it a lower specific gravity. The ammunition is charged with "ball powder". The primers are sealed and crimped in placed. The bullet is also crimped in place and the case mouth is sealed with an asphalt sealant.





Chronograph data for the IMI M855 was obtained using an Oehler 35P with "proof screen" technology. All velocities listed are muzzle velocities as calculated from instrumental velocities using Oehler's Ballistic Explorer software program. All strings of fire consisted of 10 shots each.





This accuracy evaluation used statistically significant shot-group sizes and every single shot in a fired group was included in the measurements. There was absolutely no use of any group reduction techniques (e.g. fliers, target movement, Butterfly Shots).

The shooting set-up will be described in detail below. As many of the significant variables as was practicable were controlled for. All shooting was conducted from a concrete bench-rest from a distance of 100 yards (confirmed with a laser rangefinder.) The barrels used in the evaluation were free-floated. The free-float handguard of the rifle rested in a Sinclair Windage Benchrest with the aid of a Sinclair fore-arm adaptor, while the stock of the rifle rested in a Protektor bunny-ear rear bag. Sighting was accomplished via a Leupold VARI-X III set at 25X magnification and adjusted to be parallax-free at 100 yards. A mirage shade was used.  Wind conditions on the shooting range were continuously monitored using a Wind Probe. All rounds were fired from the magazine. Each upper was fired using the same lower.


The barrels used in this evaluation were both Colt HBARs with NATO chambers and chrome lining. The 1:7” twist barrel was 20” in length and the 1:9” twist barrel was 16” in length. I purposely selected the shorter barrel with a 1:9" twist and the longer barrel with the 1:7" twist in order to exacerbate any possible statistically significant influence that the differing twist rates and intendent muzzle velocities might have on the precision of the M855 ammunition.

The first barrel used in testing was 16” Colt HBAR with chrome-lining, a NATO chamber and a 1:9” twist. This is the barrel found on the Colt 6721. All of my free-floated Colt 6721 barrels have turned in sub-MOA 10-shot groups at 100 yards when using match-grade hand-loads.

The second barrel used in testing was a 20” Colt HBAR, also with chrome-lining, a NATO chamber and of course a 1:7” twist. I've owned three of these barrels and they have all turned in 10-shot groups at 100 yards that hover just above one MOA when free-floated and shooting match grade handloads.



Three 10-shot groups were fired from the upper with the 1:9” twist barrel in the manner described above. The extreme spreads for those groups measured:

2.72”
2.19”
2.24”

for a 10-shot group average of 2.38”. The three 10-shot groups were over-layed on each other using RSI Shooting Lab to form a 30-shot composite group. The mean radius for the composite group was 0.76”.



In the same manner as above, three 10-shot groups were fired from the upper with the 1:7” twist barrel. The extreme spreads of those groups measured:

2.14”
3.01”
1.71”

for a 10-shot group average of 2.29”. As before, the three 10-shot groups were over-layed on each other using RSI Shooting Lab to form a 30-shot composite group. The mean radius for this composite group was 0.68”.





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Define "light bullets."

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Certainly. Thats generally true of barrels of any twist, though, which causes people to incorrectly attribute their experience to twist rate, especially when a small sample size is involved. If someone has a Bushy, a Colt, and a PSA, and they shoot a handful of three-shot groups, with garbage ammo, they might conclude that the Bushy is more accurate. And they might be right. Or not. But if they conclude that the Bushy is more accurate with their favorite brand of fake M193 because of its 1/9 twist, then that would be incorrect.

I’ve been told that both 1/7 and 1/8 twist marked barrels have a tendency to be 1/7.7”. @Molon , any truth to that?

No there isn't any truth to it.  That ignorant BS was started by one of the tards here on ARFCOM.  He was too stupid to know that Krieger actually makes barrels with a 1:7.7" twist and he just pulled the claim out of his ass that manufacturers were just stating that their barrels were 1:7" twist barrels when they were "really" 1:7.7" twists.  Then other ignorant people started regurgitating what he had said as if it was a fact.





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Thanks.

A lot of this silliness in the general public about twist rates came about because of Soldier of Fortune magazine articles back in the early 80s. There were a few articles about 5.56mm becoming a NATO standard cartridge and how all the pussy Europeans wanted the 62gr. SS109 ammo for humanitarian reasons. Ed Ezell also discussed this in the 12th Ed. of Small Arms of the world.

The blah...blah.....blah of the gun magazine pontificators in the early 80s was that:


55gr. American ball out of 1/12 twist barrels caused excessive injuries from tumbling & frag. = America Hell Ya! (slower twist is more devastating)

62gr. FN European ball out of 1/7 was more humane because of icepick = Europe is gay (fast twist is not as lethal)


The whole thing is stupid.

I think if I gave you a 1:7 and a 1:8, (and maybe even a 1:9, but definitely the former two)

And had you shoot a bunch of different ammo at 100 yards increments out to 500 yards, we would be very hard pressed to tell what barrel was in use on each target

They are wrong.

M856 will fit in an M16 magazine . . .

I generally preface that with “any conventional bullet that can be loaded to magazine length.”

But I’m sure there’s an exception out there I’m unaware of.

To each their own, but I have no plans to ever use tracers and at 3k+ feet of elevation 1-8 is plenty.  Best group I've ever shot was with 77 gr SMKs out of a 1-9 223.

300 yards in a 3-5 mph breeze:
Attached File

I love it when @molon releases a smack down.

I suggest we collect funds to pay for his blood pressure meds...and beverages of his choosing...because the amount of derp on these forums must drive this man insane!

I'll try to touch on a few subjects that I've seen in this thread so far...

Spinning faster and accuracy (Precision, really)--  From a physics standpoint spinning faster should on average produce worse precision.  If you know the proper inputs, 6DoF models can predict this behavior.  If a bullet-- even a theoretically perfectly manufactured bullet-- starts into the rifling crooked and is deformed such that it is in the bore spinning about an axis that is not the centerline axis of the bullet before deformation, it will cause it not to fly to the same place as one that is aligned with the bore.  If a bullet is manufactured with some eccentric mass (jacket runout, core runout, dings, etc..) it will contribute to variation in POI.  The faster you spin those imperfections, the greater their effect will be on dispersion.  HOWEVER...  Not all barrels are created equally, and there are a lot of contributing factors to the subject of dispersion.  So individually you will see barrels of high quality that have fast twists and slow twists and they will both shoot decent-to-excellent bullets very acceptably.  "All else being equal" (which never happens in the real world), though, a faster twist barrel should have worse dispersion.  In the real world the great many factors at play often are of greater magnitude than the singular effect of faster RPM by itself and those factors add or subtract to make the results of "twist rate vs. precision" tests very muddy.

RPM vs. Fragmentation--  This is less of a direct correlation than many may think.  The tendency of slower RPM FMJ style bullets to fragment is not because of the RPM, it's that the slower RPM has a lower gyro stability.  That lowered gyro stability means a longer yaw precession cycle, and in the event that something happens upon muzzle exit to induce an initial angle of attack, it will recover much more slowly.  Down range, bullets that impact a target (Gel, tissue, whatever) at a higher angle of attack will upset and yaw more rapidly and increase the chance that they fragment or fragment sooner.  It's more of an AoA vs. fragmentation correlation.  If that slow twist bullet happens to get launched straight with no initial AoA, it will still pencil through quite a ways without rapid upset/yaw.

RPM vs. expansion--  Very minimal effect for bullets designed to expand.  This is primarily driven by velocity.  HOWEVER, spinning faster than what a bullet was designed to take can cause terminal performance failures due to jacket petals shearing where they would have otherwise held together.  This can result in inconsistent performance, shallower penetration, or complete integrity failures.   I doubt you'll see much difference in a .223/5.56.  An extreme example is something like the 8.6 BLK, where it sports a 1:3" twist barrel, and the .338 diameter hunting bullets that are absolutely solid performers at much greater velocities with 1:10" twists , can blow up and not work as advertised even at the bottom end of the expansion velocity envelope.

RPM/Gyro vs. BC/Cd-- From a stability standpoint, if the mass and aero characteristics of the bullet are known (not all free-use estimation tools out there are as accurate  as we'd like them to be), then a Gyro stability factor of over 1.0 will be "stable".  Less than 1.0 will start high AoA flight and will not recover.  However, from a gyro of 1.0-1.1 typically you see pretty significant angle of attack (BIG yaw cycles) persist until the bullet slows down and becomes more stable.  By the time it fully recovers the damage is done for dispersion.  Usually more of a shotgun pattern of sorta-round holes in paper.  Bullets that launch with a SD of 1.2-1.5 are considerably better off.  These bullets are capable of extremely good precision, but still have some AoA that increases drag (lowers BC).  Over about 1.5 SD gets you most all of the BC potential.

In-flight integerity-- In exceptionally rough/long bores, in hot temps, with thin jackets, excessive oil, and/or very fast twist rates (~300,000rpm or faster), you can cause bullets to blow up mid-flight.  It's not a hard line in the sand and there are many contributing factors.  The failure is a combination of centrifugal forces of the core trying to escape the jacket, the core surface melting and slipping, or the jacket simply failing.


Anyway, theoretical arguments are mostly dumb. Worry about real life.  With everything I briefly touched on above there is books worth of nuance and individual case-by-case variation.  1:8" or 1:7" or anywhere in between will stabilize most any bullet you're going to magazine-feed from a .223/5.56.  Even 1:9" gets most of the stuff that's not at the very-heavy end. 1:8" is my easy button, personally.  Barrel and bullet quality trump most things for accuracy.  Don't over think it.

To give people a visual perspective of why M856 requires a fast twist . . .





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