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The spin on .223 twist rates: 1:7? 1:9? One-in-whatever? What's the real dope on the subject of "stabilizing influences?".

EVEN AS A GUNWRITER CONTINUALLY INTERACTING WITH THE FIREARMS INDUSTRY, I COME ACROSS INFORMATION THAT'S NEW TO ME on an almost daily basis. For example, not too long ago I learned that the original M16 had a twist rate of 1:14. I'd thought it was 1:12 (the twist was in fact later increased to 1:12), but, either way, that got me thinking. Many armchair and Internet commandos today argue that any AR with a twist slower than 1:7 (the current military twist rate) is only suitable for shooting the side of a barn--from inside it. Even 1:9 AR barrels are currently looked at with derision by most of the "tacticool" crowd. Anyone admitting on an Internet forum that he owns an AR with a 1:9 barrel is harassed, as "everyone" knows they cause toenail fungus, halitosis and impotence.

Whether we're talking .223 barrels with a 1:7 or 1:9 twist, both are a far cry from the MI6's original 1:14 or its replacement, the 1:12. With the popularity of both the AR-15 and the .223 cartridge, there is a wide variation of available bullet weights in both loaded ammunition and components. The question I had was this: How much difference does twist rate actually make? This would require a test of not just different barrel twists, but bullet weights.

A brief primer on .223 barrel twist rates: Faster twists are generally required to stabilize longer, heavier bullets. The original M16 1:14 twist was designed to barely stabilize a 55-grain bullet. It worked fine in certain environments but not in others, which was why it was replaced with a 1:12 in the M16A1. When the military switched from a 55-grain bullet to a noticeably longer 62-grain projectile (the M855), they increased the twist rate to 1:7. The faster the twist rate of a barrel, the more resistance the bullet encounters while traveling down it. This can result in higher pressures and/or higher velocities, depending on the gun and barrel length. It will also speed up the wear on your barrel, but most people won't shoot enough to notice. Instead of accuracy starting to degrade after 15,000 rounds, groups from a 1:7 barrel might start expanding after only 10,000 rounds.

The lion's share of .223 barrels available today--whether we're talking bolt-action rifles or semiautos--have either 1:7 or 1:9 twists. To do some testing, I acquired two rifles from Savage, both Model 12 Varmints with laminated stocks and 26-inch fluted stainless barrels. They are identical except for twist--one has a 1:7 barrel, the other has a 1:9. As a huge number of .223s in this country are fired out of ARs, I also acquired a rifle for testing from Alexander Arms. The first has a 20-inch fluted stainless barrel with a 1:9 twist. The company also sent me a second top end with a 16-inch fluted stainless barrel with a 1:7 twist.

Upon first opening the box of the first Savage, I realized I've been spending too much time with black rifles. The Savage was simply beautiful, a piece of functional art. The grain of the stock was gorgeous, and the stock on the second rifle was just as pretty. Bolt action was smooth with very little play. Trigger pulls on both bolt guns were excellent, due to the Savage Accu-Trigger system. Crisp and just a hair over two pounds, they allowed me to shoot up to the rifles' potential--well, minus the ultrasonic skeletal vibration I've been nurturing with my Diet Coke LV. drip.

Alexander Arms just recently started making AR-15s in conventional calibers, having made their bones with oddball ones like the .50 Beowulf and 6.5 Grendel, as well as their newest venture, ARs in .17 HMR. The rifle and spare top end I acquired for testing are actually chambered in 5.56 NATO, which works fine for .223. What's the difference? Dimensionally, none, but the 5.56 is loaded to slightly higher pressures. 'The rifle was equipped with AA's standard "tactical trigger," a single-stage design that provides a crisp, 4 1/2-pound pull.

[ILLUSTRATION OMITTED]

[ILLUSTRATION OMITTED]

Following the weird nonlogic of the firearms world, the bullets used in the .223 Remington/5.56 NATO are actually .224 in diameter. The range of bullet weights available in that caliber is vast, from tiny, 35-grain, thin-jacketed varmint zappers to 90-grain match BTHPs. Factory ammunition is loaded to the SAAMI-spec overall length of 2.26 or shorter, and the AR-15 magazine is designed around cartridges that length. The heaviest bullets you'll find in loaded ammunition, which will fit inside an AR magazine (just barely), are 77-grainers. If you try to stuff a heavier bullet deep enough into a case to make that 2.26 length, all sorts of things start going wrong. Depending on the length of ogive, some 75- and 77-grain bullets are too long and won't allow you to sneak inside that AR magazine. Loading cases with anything heavier than 77-grain bullets will guarantee their overall length is too long to work with even in most bolt-action rifle magazines, and they'll have to be single-loaded into the chamber.

Why use heavy-for-caliber bullets? They do much better bucking the wind at distance. Black Hills helped develop the Mk 262 round for the U.S. military, which features a 77-grain OTM bullet loaded to AR mag length. That was quite an accomplishment, and the story behind that cartridge is interesting enough for a separate article. This heavy bullet has been found to not just be more accurate at distance in Afghanistan, but more effective on enemy combatants. Camp Perry and target shooters have found 80-and 90-grain bullets much preferred on the 600-yard line.

[ILLUSTRATION OMITTED]

For this project I ordered a number of different bullet weights from both Sierra and Hornady. The heavier projectiles came with twist rates recommended right on the boxes-1:7 to 1:10 for the 65-grain spitzers from Sierra, 1:8 for the Hornady 75-grain BT, 1:7 to 1:8 for the Sierra 77-grain HPBT, and 1:6.5 for the Sierra 90-grain HPBT. Following the twist-rate recommendations on the Sierra bullet boxes was the word "only" in red. But part of what I wanted to discover was what would happen if I didn't follow those recommendations.
FACTORY AMMUNTION

ALEXANDER ARMS
(20-IN.BBL.,
1:9 TWIST)

LOAD                  BULLET  VELOCITY  STD.  AVERAGE
                 WEIGHT(GR.)     (FPS)  DEV.    GROUP
                                                (IN.)

HORNADYNTX                35     3,813    33     1.33

BLACK HILLS FMJ           55     3,112    22     1.40

FEDERAL BTHP              69     2,788    31     1.44

HORNADYBTHP               75     2,755    34     2.31

BLACK HILLS OTM           77     2,734    21     1.31

ALEXANDER ARMS
(16-IN. BBL,
1:7 TWIST)

HORNADYNTX                35     3,622    31     1.41

BLACK HILLS FMJ           55     2,987    23     1.79

FEDERAL BTHP              69     2,681    34     1.64

HORNADYBTHP               75     2,615    37     1.73

BLACK HILLS OTM           77     2,614    19     1.68

FACTORY AMMUNITION

ALEXANDER ARMS
(20-IN. BBL, 1:9
TWIST)

BULLET/WEIGHT (GR.)  CHARGE    COL  VELOCITY  STD.  AVERAGE
                     WEIGHT  (IN.)     (FPS)  DEV.    GROUP
                      (GR.)                           (IN.)

SIERRA BLITZKfNG/40      25   2.20     3,674    23     1.38

SIERRA 5PITZER/55        25   2.25     3,108    21     1.45

SIERRA 5PfTZER/65        23   2.25     2,899    27     1.35

HORN. A-MAX/75         22.5   2.39     2,805    24     1.82

5IERRA BTHP/90         21.6   2.55     2,522    18     6.28

ALEXANDER ARMS
(16-IN, BBL, 1:7
TWIST)

SIERRA BUTZKING/40       26   2.20     3,567    27     1.43

SIERRA SPITZER/55        25   2.25     3,022    23     1.57

SIERRA SPITZER/65        23   2.25     2,743    33     1.34

HORN. A-MAX/75         22.5   2.39     2,683    14     1.52

SIERRA BTHP/90         21.6   2.55     2,581    18     2.65


It was interesting to me that while the 35-grain Hornady NTX and 40-grain Sierra BlitzKing are both light for caliber, there was no caution on the boxes about what twist rates they should be fired through. Why? Because spinning a bullet faster than it requires to stabilize doesn't harm anything.

[ILLUSTRATION OMITTED]

I talked with a lot of people smarter than me, including Bill Alexander of Alexander Arms. While I didn't have time to actually try it myself, Bill told me that I would see a distinct difference in both accuracy and velocity between button-rifled stainless steel AR barrels and standard chrome ones, all other things being equal. In fact, there are so many things that affect accuracy and velocity (especially in semiautos) that I tried to eliminate as many variables as possible.

When handloading, I used only new Homady brass, Winchester Small Rifle primers and Alliant Powder's relatively new AR-Comp powder. From the name you can probably guess it was designed specifically for loading .223/5.56 for use in AR-15s. The Alliant reloading guide had "recipes" for bullet weights from 52- to 90-grain bullets, and I adjusted accordingly when loading for the lighter 40-grain bullets I had on hand (don't try that at home). I was not trying to develop max-pressure loads, just consistent ones to judge accuracy and velocity and so loaded everything a little light.

[ILLUSTRATION OMITTED]
Savage model 12
Varmint (26-in, bbl,
1:9 twist)

Load                   Bullet  Velocity  Std.  Average
                       Weight     (pps)  Dev.    Group
                        (gr.)                    (in.)

hornaovntx                 35              32     0.98

black hills fm             55     3,159    22     0.84

federalbthp                69     2.874    29     1.02

hornadybthp                75     2,813    30     1.11

black hills otm            77     2,774    19     1.22

savage model 12
VARMINT (26-IN, BBL.,
1:7 TWIST)

hornady ntx                35     3,972    29     0.93

black hills fmj            55     3,162    23     0.92

federalbthp                69     2,864    25     0.98

hornadybthp                75     2,831    38     1,08

black hills otm            77     2,788    19     0.89

SAVAGE MODEL 12
VARMINT (26-IN, BBL.,
1:9 TWIST)

BULLET/WEIGHT (GR.)      POWDER   COL
(IN.)                  VELOCITY  STD.  AVERAGE
                         CHARGE          (FPS)  DEV.  GROUP

                          (CR.)                       (IN.)

SIERRA BLITZKING/40          26  2.2D    3.859    29   1.08

SIERRA 5PITZER/S5            25  2.25    3,224    23   0.95

SIERRA SPITZER/65            23  2.25    2,951    37   0.89

HORNADY AMAX/75            22.5  2.33    2,889    22   0.99

SIERRA BTHP/90             21.G  2.55    2,601    18   6.45
SAVAGE MODEL 12
VARMINT (26-IN. BBL.,

1:7 WIST)
JLIRRA BLITZ K1N             26  2.20    3,866    41   1.21

G/40

SIERRA SPITZER/55            25  2.25    3,187    28   1.05

SIERRA SPITZER/65            23  2.25    2,972    29   0.35

HORN ADY A-MAX/75          22.5  2.39    2,933    24   0.97
5IERRA BTHP/90             21.6  2.55    2.613    23   1.45

All ammunition used was .223 Remington. All handloads loaded on
new Hornady brass with Winchester Small-- Rifle Primers using Alliant
AR-Comp powder. Accuracy results are the averages of four five-shot
groups at 100 yards from a sandbag rest. Velocities are averages of
10 shots measured with an Oehler Model 35P 12 feet from the muzzle.


The 77-grain Sierra BTHP has been successfully loaded to 2.26-inch AR-mag length (see Black Hills' Mk 262 above), but loading both the 75-grain Hornady A-MAX and the 90-grain Sierra BTHP to fit inside either the AR magazines or the Savage magazine was a no-go. The 75-grain rounds I loaded to a 2.39-inch OAL and the 90-grainers to 2.55. For testing, I had to single-load them into the Savage's chamber.

[ILLUSTRATION OMITTED]

After spending a lot of time handloading, I was able to head out to the range. For accuracy testing I used a 4.5 X-14 X-42mm Burris MTAC scope, which has the company's G2B Mil-Dot reticle. I like Burris scopes, as they have good glass, hold zero and don't require you to sell your first-born to afford one (not that anyone would buy my kids ...).

It would be lying to say that I didn't have some expectations when I started pulling the trigger, but what I was expecting didn't happen--neither the bolt guns nor the ARs in 1:7 or 1:9 showed any distinct preference for any bullets weighing between 35 and 77 grains--with two exceptions. The 1:9 Alexander Arms rifle didn't like the 75-grain A-MAX, and the 1:9 Savage didn't like the Black Hills 77-grainers, but that was it. There was no predictability to the accuracy results--the two most consistently accurate loads across the board were the 35-grain NTXs from Homady and the 77-grain Black Hills loading. Think about that. That's a 42-grain difference--one bullet more than double the weight of the other--and yet they both performed.

When it came time to load the 90-grain rounds I'd put together ... well, that was interesting.

Both the Savage and Alexander Arms guns with 1:7 twists shot these heavy bullets, but not as accurately as the lighter projectiles. Loading them into the 1:9 guns ... wow. I'd heard of keyholing and seen it happen once or twice because of damaged barrels, but every 90-grain bullet I fired out of the 1:9 barrels started yawing and hit the targets sideways. While I did my accuracy testing at 100 yards, I moved the targets closer just to see and found that the long 90-grain bullets had already started yawing badly at 50 yards. The 1:9 twist rate was just not fast enough to stabilize them. Period. The targets looked like they'd been peppered with shrapnel.

[ILLUSTRATION OMITTED]

ARs with 1:12 barrels are notorious for sending 62-grain M855 bullets downrange sideways. I've seen some AR-15s with 1:9 barrels that shoot 77-grain bullets great at 600 yards, while others with match barrels will struggle to keep those same bullets into a coffee can at 200 yards.

Conclusions? The vast majority of all .223/5.56 ammunition sold in this country features projectiles at or around 55 grains in weight, so whether you have a 1:7 or 1:9 barrel, the twist shouldn't make a difference in your accuracy. When it comes to those barrels, the minor quirks in the individual barrels seem to affect accuracy more than the twist rate, at least when it comes to most ammo.

However, when you start shooting bullets weighing at or over 65 grains, there's no guarantee what kind of accuracy you're going to get if your barrel doesn't have a twist faster than 1:9. All barrels seem to show a preference for one type of ammo or another, and there doesn't seem to be any way to predict it or explain it. I've seen two bolt-action match rifles from the same custom maker shot side by side--one loved a certain load and would shoot one-hole groups all day long, while the other one didn't like it at all.

We're living in the golden age of firearms and have gotten so spoiled we don't realize it. I wasn't surprised--but rather expected--that the Savage rifles with their excellent triggers would shoot sub-MOA with most ammo. And that neither of the Alexander Arms ARs even came close to jamming--even with the wide variety of bullet weights.
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Author:Tarr, James
Publication:Guns & Ammo
Geographic Code:1USA
Date:Feb 21, 2013
Words:2534
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