AR-15 Barrel Twist Rates – What You Need To Know

By Tom McHale
Tom explores the importance of AR-15 Barrel Twist Rates. What can go wrong & what can go good.

AR-15 Barrel Twist Rates
AR-15 Barrel Twist Rates
Tom McHale headshot low-res square
Tom McHale

USA –-(Ammoland.com)- There's more misunderstanding surrounding AR-15 barrel twist rates than the electoral college’s secret faculty lounge and doomsday bunker under the Denver International Airport. That’s because, as with any complex topic, there's plenty of myth wrapped around some nuggets of truth.

That blend of fact and fiction is what makes the topic mysterious to so many.

We decided to embark on a little experimentation to put some of the common assumptions to the test. When buying a common AR-15 barrel, what do you have to worry about given the type of shooting you intend to do? What types of ammo should you use, or not use, for your particular barrel? Will choosing the wrong twist rate for your AR-15 cause the moon to plummet into the Toad Suck, Arkansas State Park? With some help from our friends at Stag Arms, we decided to explore the topic a bit more.

What are Barrel Twist Rates?

As a quick level setting refresher, the twist rate of a rifle barrel refers to the speed at which the rifling imparts spin to the projectile. A more aggressive rifling pattern, represented by a faster twist rate, will turn the bullet more for each inch of travel down the barrel thereby resulting in a faster spin rate. With most modern AR rifle barrels you'll hear the AR-15 barrel twist rates expressed in terms like 1:7 or 1:9. The first number refers to one full rotation of a bullet. The second number refers to how many inches of barrel length it takes to make that one full rotation. For example in a 1:7 twist barrel, the bullet travels 7 inches down the bore before it makes a full rotation. In a 1:9 twist barrel it takes 9 inches to turn the bullet around one full-time.

What better way to test out twist rate theories than using two identical uppers. These complete upper assemblies from Stag Arms Model 3TH-M Uppers feature 1:7 and 1:9 twist rates.
What better way to test out twist rate theories than using two identical uppers. These complete Stag Arms Model 3TH-M Uppers assemblies from Stag Arms feature 1:7 and 1:9 twist rates.
As a side note, I loved these Diamondback hand guards on the Stag Arms Model 3TH-M Uppers. Very cool!
As a side note, I loved these Diamondback hand guards on the Stag Arms Model 3TH-M Uppers. Very cool!

Why are AR-15 Barrel Twist Rates Important, What Can Go Wrong?

The goal of all this twisting is to stabilize a bullet in flight. Just like a football, a bullet has to spin to fly straight and true over distance. How fast it needs to spin to maintain perfect stability throughout its flight path depends on a whole lot of factors like velocity, bullet diameter, bullet weight, shape, and weight distribution within the bullet itself.

Here's where things start to get weird. There are several theories about what can go wrong if an ar15 barrel's twist rate and specific bullet attributes don't match up properly. And like all theories, there's usually some truth involved, and that makes the myths all the more persistent.

First, if a bullet doesn't spin fast enough, it won't be stable. Like throwing a football end-over-end, it will fly all wobbly, to the point of not really “flying” at all. The bottom line is that it won't do what it's designed to do – fly predictably. You may have even seen targets with oblong holes in them from a bullet impacting sideways. That can happen as we'll soon see.

You might also hear about over-twisting a bullet. In theory, if you spin a given type of bullet too fast for its design parameters, it can fly apart in mid-air. It sounds crazy but think of this like a flywheel on a piece of mechanical equipment. If you spin it too fast for its construction and materials limitations, it will self-destruct by flying apart. If that example is too obscure, go out into your front yard, grab a friend by the arm and spin them around you as fast as you can. Eventually, they’re going to launch right into the neighbors recycling bin. In a less extreme scenario, an over-rotated bullet may self-destruct on contact with virtually any target, even a soft one, because it's on the verge of coming apart at the seams.

I loaded some seriously goofy AR-15 rounds for our AR-15 Barrel Twist Rates project. The things we do for science...
I loaded some seriously goofy AR-15 rounds for our AR-15 Barrel Twist Rates project. The things we do for science...

Twist Rate Considerations

For everything to work just right, you need to match bullet types and barrel twist rates. Normally people talk about bullet weight being the deciding factor. That's not entirely true. For example, consider civil war rifle barrels. They might use twist rates as slow as one rotation in 78 inches to stabilize a heavy musket ball. The spherical shape makes them short for their weight, so a fast spin was not needed. The primary concern is bullet length, but that usually corresponds pretty closely with weight, hence the confusion.

Longer (and usually heavier) bullets require a faster twist rate because they tend to be more inherently wobbly. Shorter (and lighter) bullets don't need as much spin to stabilize so slower twist rate barrels work fine for those.

When you buy an AR-15 chambered in 5.56mm NATO or .223 Remington, you’ll typically see one of the following twist rates on the barrel: 1:7, 1:8, or 1:9. While you might find other twist rates on certain rifles, like 1:12, those first three are now the most common.

As a side note, you will see differences on bolt-action rifles in .223 Remington as those are often optimized for lighter varmint bullets. Here, we’ll stick to AR-15 barrels.

The 80-grain bullets are too long for AR-15 magazines and had to be loaded singly into the chamber.
The 80-grain bullets are too long for AR-15 magazines and had to be loaded singly into the chamber.

To clarify what's real and what's a myth we decided to do a little testing by loading up some bullets at the short and long extremes and firing them through two nearly identical STAG Arms upper receivers. We used the Stag Arms Model 3TH-M Uppers, ready to go with bolts, carriers, and the exceptionally badass Diamondhead VRS-T handguards. These barrels share the same construction method, were made in the same shop, and only differ by twist rate. One was a 1:7 twist while the other features the slower 1:9 twist rate.

We didn’t bother with a 1:8 twist rate barrel because they’re designed to shoot everything, so that was unlikely to illustrate any odd behavior.

Safety First!

Experimenting with stuff like this can be dangerous. All loads concocted for this article were within published guidelines and shooting tests were done under controlled conditions. We did everything at a proper outdoor range and started from short distance so we could be certain that any unstable or fragmenting bullets were trapped by the very large backstop directly behind the target.

As you’ll see, that turned out to be a good thing, as some load and barrel combinations proved uncontrollable.

Weird Science

I loaded up two different types of .223 Remington ammo at extreme ends of the bullet length and weight spectrum. Using all once-fired Lake City Brass, I loaded a batch of ammo using Hornady 35-grain V-Max bullets for the short and light sample. These are stubby little bullets intended for bolt gun varmint loads, but we’re doing weird science, right? For the long and heavy sample, I loaded a bunch of Hornady 80-grain A-Max bullets.

I should note that these bullets are not designed for semi-automatic use – the overall cartridge length is too long to fit in a standard magazine so they must be singly loaded in the chamber. The sacrifices I make for science…

I loaded up a couple of batches of .223 to represent the bullet length and weight extremes using Hornady 35-grain V-Max and 80-grain A-Max bullets.
I loaded up a couple of batches of .223 to represent the bullet length and weight extremes using Hornady 35-grain V-Max and 80-grain A-Max bullets.

With bullets and uppers in hand, I headed to the range to see what happens with these loads in various scenarios. I started everything at a short distance of 25 yards. If things were going to get weird right out of the muzzle, I wanted to be right up against a big backstop for safety purposes. The short range would also allow me to keep weirdly behaving bullets on paper so I could see what happened. Depending on short range results, I would move to the rifle range for stage two.

Here’s what happened.

1:7 twist rate, 25 yards, 35-grain bullets

This tested the theory of over-rotation. I clocked velocity of these guys at an average of 3,216 feet per second using a Shooting Chrony Beta Master Chronograph placed 15 feet in front of the muzzle. Doing some quick math, I figured the revolutions per minute (RPM) of these rounds at about 330,788. That’s some serious spin considering your car engine screams bloody murder when it gets to 6,000 or so.

To put in in perspective, the blades in a jet turbine spin in the range of 8,000 to 15,000 rpm.

Check out this non-group from 35-grain bullets fired from the 1:7 twist barrel at just 25 yards. Impacts spread across two 12-inch target squares.
Check out this non-group from 35-grain bullets fired from the 1:7 twist barrel at just 25 yards. Impacts spread across two 12-inch target squares.

I fired at a 12-inch square target 25 yards away and was lucky to be on paper. Five shots later, I walked out to inspect the target and found some pretty interesting results. My group, if you want to call it that, covered an area 14 inches tall and about eight inches wide. Not a single bullet hole was round, indicating either contact fragmentation from cardboard impact or perhaps weird tumbling. I suggest fragmentation because the target showed evidence of fragments hitting the paper separately from the primary holes. The other clue was that the holes weren’t “keyhole shaped” as we saw later in the test, but jagged, random, hot messes, kind of like a Kardashian family reunion.

Not only did bullets fly all over the paper, there was evidence of mid-air fragmentation. The bullets that did make it to the paper either blew up on contact or hit really weird. All the holes were ragged and random.
Not only did bullets fly all over the paper, there was evidence of mid-air fragmentation. The bullets that did make it to the paper either blew up on contact or hit really weird. All the holes were ragged and random.

Given the randomness of the short range performance of these short light bullets from a 1:7 twist rate barrel, I had to stop at 25 yards because bullets would have never stayed on the backstop from 100 or more yards. If you want to hit absolutely nothing, this load could be an option!

1:7 twist rate, 25 yards, 80-grain bullets

This combination worked just fine. I clocked velocity at 2,541 feet per second and proceeded to shoot at the 25-yard target. This combination of long and heavy bullet with a fast twist rate barrel was supposed to work, and it did. Bullets went right where they were supposed to, made nifty perfectly round holes, and grouped nicely.

By the way, the rpm of these bullets are about 261,360.

As expected, the 80-grain bullets worked as expected from the 1:7 twist barrel at 25 yards.
As expected, the 80-grain bullets worked as expected from the 1:7 twist barrel at 25 yards.

1:9 twist rate, 25 yards, 35-grain bullets

This combination was probably supposed to work also. I only say probably because these teeny, tiny bullets are most likely better suited for bolt gun barrels with a 1 in 12-inch twist or something along those lines. As it turned out, the 1:9 Stag Arms barrel on the 3TH-M Uppers Halve worked just fine, at least at 25 yards. The bullets made a one hole group with nice round holes and impacted where the scope said they would.

Since we got all math geeky with the 1:7 barrel, I’ll mention that this combo spun the bullet at about 257,280 rpm.

As expected, the 35-grain bullets worked like a champ from the 1:9 barrel at 25 yards.
As expected, the 35-grain bullets worked like a champ from the 1:9 barrel at 25 yards.

1:9 twist rate, 25 yards, 80-grain bullets

According to the warnings from ammo and rifle manufacturers, this is not supposed to be a workable combination, but in the name of science, I wanted to see exactly what happened. As ESPN’s Chris Berman would say, we had some rumblin', bumblin', stumblin’ bullet performance. My 25-yard group measured about 10 inches wide by six inches tall. The best part was the nifty bullet profiles in the target. Every single bullet impact made an oblong, bullet-shaped hole, just as if the rifle tried to launch them completely sideways. Clearly, as soon as these lumbering 80-grainers left the barrel, they started to tumble end over end. Interesting, but probably not very useful for long range precision shooting. Needless to say, I had to end this particular combination at the 25-yard range as well as there was no telling where bullets would fly on the longer rifle range.

The long and heavy 80-grain bullets were all over the target at just 25 yards.
The long and heavy 80-grain bullets were all over the target at just 25 yards.

Our spin rate for this final combination was somewhat leisurely, operating at just 203,280 rpm.

Every 80-grain bullet tumbled when fired from the 1:9 twist barrel at just 25 yards.
Every 80-grain bullet tumbled when fired from the 1:9 twist barrel at just 25 yards.

1:9 twist rate, 100 and 200 yards, 35-grain bullets

At 100 yards, the light bullets in the 1:9 twist barrel worked reasonably well. Two different five-shot groups fired from 100 yards measured 1.17 and 1.48 inches. I also shot these at 200 yards. It was a windy day, so that might have impacted group sizes a bit.

The 35-grain bullets shot well at both 100 and 200 yards from the 1:9 twist barrel.
The 35-grain bullets shot well at both 100 and 200 yards from the 1:9 twist barrel.

 

Even on a windy day, I got decent groups from the 35-grain bullets at 200 yards from the 1:9 twist barrel.
Even on a windy day, I got decent groups from the 35-grain bullets at 200 yards from the 1:9 twist barrel.

1:7 twist rate, 100 and 200 yards, 80-grain bullets

Groups using the extra-long 80-grain A-Max bullets were predictable if not small. At 100 yards, I was getting 3.12 inches center to center and at 200, a little better with 4.83 inches. From the 1:9 barrel performance, I know the Stag Arms barrels are capable of solid accuracy, so I would guess it was my particular load combination that opened the groups a bit. With a dozen or so powders and hundreds of charge weight, powder, primer combinations, I’m sure I could have found a good load that generated better accuracy. But since the goal here was to see if the combination of bullet and barrel yielded predictable performance, I didn’t go down that road. The bullets were predictable using the 1:7 twist barrel as they were supposed to be.

Groups at 100 yards were predictable with the 80-grain bullets. Since this test wasn't about accuracy, I didn't spend any time experimenting with different powders or charges.
Groups at 100 yards were predictable with the 80-grain bullets. Since this test wasn't about accuracy, I didn't spend any time experimenting with different powders or charges to tighten up my groups.

Summing Things Up

As a quick and dirty “control” I also shot Sig Sauer 77-grain match ammo through both barrels at 25 and 100 yards to see how the more commonly available ammo worked. At 25 yards, the 1:7 twist rate barrel shined, creating a near one-hole group just where expected. Using the 1:9 twist barrel, which is NOT recommended, I had some vertical stringing at 25 yards, but things weren’t completely random, so I felt confident shooting at 100 yards too.

Moving out to the 100-yard range, the 1:7 barrel gave me a perfectly normal 1.58-inch group with the Sig Sauer 77-grain ammo. Four of the five shots were touching, so the flyer that opened the group up to 1.58 inches might have been shooter error. Using the 1:9 barrel, I got a perfectly normal group as well, with three shots measuring .66 inches. I didn’t want to press my luck in case there was any weird performance, so I only shot three, checking each one.

Again, this isn’t a recommended configuration, so don’t replicate it at home.

You’ll notice that I didn’t shoot any 55-grain bullets in either barrel. That’s because they’re middle of the road in terms of weight and length and will work just fine in any of these barrels. I’ve shot billions and billions of 55-grain bullets of varying types through 1:7, 1:8, and 1:9 barrels and not yet seen weirdness in any of them.

With the right bullets matched to the right twist rate, the Stag Arms barrels will shoot as shown by this control group using 77-grain Sig Sauer Match ammunition.
With the right bullets matched to the right twist rate, the Stag Arms barrels will shoot as shown by this control group using 77-grain Sig Sauer Match ammunition.

I should note that I wanted the shortest and lightest bullets I could find for this test, and that turned out to be Hornady V-Max. These are designed to have light jackets and blow up on contact with varmints, so they’re (again by design) more likely to blow up mid air when over-rotated. I’m sure there are short and light bullets out there that would not self-destruct when fired through a 1:7 barrel.

You can’t blame everything on the barrel. Non-concentric bullets are going to exhibit more random behavior at the edge of stabilization parameters than quality bullets that are perfectly balanced.

If you’re going to buy an AR-15 chambered in 5.56mm NATO, it’s hard to go wrong with either a 1:7 or 1:8 twist barrel for standard shooting. Those will handle a wide range of bullets safely. If you know you’re going to buy or build a varmint rifle, and you’ll be using light bullets, then you might consider one with a twist rate designed for the task, either a 1:9 or maybe a 1:12. Just be aware that if you go beyond 1:8, you’ll be limited to shooting bullets less than 60-some grains. As a practical example, I’m not a varmint guy, so all of my AR rifles are either 1:7 or 1:8 twist and I regularly shoot bullets from 50 to 77 grains with no ill effect. But once again, remember, it’s the bullet length, not the weight, that matters. Weight is just an easy way to categorize by approximate length.

Ain’t science fun?

About

Tom McHale is the author of the Insanely Practical Guides book series that guides new and experienced shooters alike in a fun, approachable, and practical way. His books are available in print and eBook format on Amazon. You can also find him on Google+, Facebook, Twitter and Pinterest.

77 thoughts on “AR-15 Barrel Twist Rates – What You Need To Know

  1. I really enjoyed the read and it helped shed light on an sbr I’m looking forward to building. Anyway, I have the same diamond head rail and need to know what are the scopes you used in this experiment?

  2. Re: In regards to the M-14, Hindsight is 20/20. I am a traditionalist, and was never able to warm up to The AR-15. Some 15 years ago, I could have purchased an M-16 for $675.00. Wold you believe: Gun purchases for investment, are also 20/20. My gun dealer, has been a friend for many years. He is not only a dealer, but a distributor, for the state of Florida. As a Class 3 dealer, he provides weapons and supplies for Law Enforcement.

    Speaking of the M-14: I have had several M-1’s over the years. My favorite was a Match Grade Harrington & Richardson in 30/06. This time I foolishly sold the H&R, for $500.00 over the price I originally paid. Never realized that a Match Grade would bring $3,000.00 +. General Patton once said: ” The M-1 is the greatest battle impliment ever divised”.

    As for the AR-15, & M-16, they have come a long way, since Viet Nam. Colt’s manufacturing process, has improved greately over the years. When the C&C machinery came of age, the quality improved greately. The C&C repeats the same process over and over without error. This is not to slight a Master Gun Smith. The Clark Sr. Bulls Eye 45cal is a masterpiece to look at and shoot. Sr’s were all hand crafted, unlike his son.

    Honestly! Change is difficult for us old folks.

  3. I am in total agreement with the Grim Reaper: Along with the Colt 45, the M-14 has no equal. In the 80’s, I had an opportunity to purchase, an unfired fully-auto M-14, in the original box for $1,800.00. I often think of the foolish decision I made, not to purchase the M-14. I suspect an M-14 in this condition today, would exceed $25,000.00. The state of Florida is a great place to live, if you enjoy collecting and shooting Class 3 weapons.

    1. Re you passing up the M-14 mentioned, we grow to soon old, to late smart might be appropriate. Of course, if you lacked the $1800 purchase price, the story changes markedly.

    2. I bought a Springfield Armory M1A back in 1980 and had serious thoughts of having it converted to select fire. After shooting it the first time I saw that full auto would not really be practical in an M1A/M14.

  4. Here is the experience of an Infantryman in 1965-66 and 1969-71. I trained on the M-14. In my opinion, it is the best infantry weapon in history. The M-16 was just coming into use so we were “familiarized” with it. We were told all kinds of stories about the devastating hydrostatic shock of the 5.56 bullet. It was almost so lethal that if you shot a private in the Mekong Delta, you would kill a sergeant in Hanoi! In Vietnam, I was issued the “little black gun.” I took it to the range to zero it although I was told that it was a waste of time — I would never see the V.C. who was shooting at me. The marksmanship philosophy prevalent in Vietnam was “spray and prey.”

    I did, contrary to common knowledge see a V.C. He was trying to conceal himself behind a bush about 25 meters away. I took three quick well-aimed shots and he fell. There was one bullet hole in his eye. I used to shoot pretty tight patterns, even quickly, so I inspected the bush he was hiding behind. In a branch about two inches wide I found two entrance holes but no exit! I immediately took the M-16 back to the armorer and traded it for a real gun.

    Several years later, in a “friendly fire” incident, one of my men was shot in the back of the hand, from about 400 meters, between the joints of his first and second finger, with an M-16. The bullet didn’t fully penetrate his skin. He pulled it out with his teeth!

    If you expect to be in a gun fight get a real gun!

    1. Your comments reminds me of a book I read about the Army LRRPs in Vietnam in the time period of 1968 to around 1969. The author mentioned that in one firefight his M-16 jammed and he then dropped it and then picked up an AK-47 from a dead VC that he had shot and then continued to fight using the AK! After the Battle he picked up the Jammed M-16 and took both the M-16 and the AK-47 back to the base. He then cleaned the HECK out of the M-16 and then went to the “Firing Range” to test it. Well the M-16 Jammed again!! That was when he decided to switch to using either the AK-47 or M-14.

      1. From just about everything I have read and heard about the M-16 and the troubles with it, it strikes me that a number of people at Colt’s as well as in “the military” would have been prime candidates for criminal prosecution re problems encountered with the M-16 rifle, at least earlier versions thereof, and this applies to BOTH the rifle and ammunition. For those interested in the history of things, I suggest reading The Gun by C.J. Chivers.

        1. Being in the DaNang area for 2 yrs; I opted for the M14, it would penetrate a 6″ bamboo or a 3″ small tree or branch and the M16 could not do it. The first M16’ss were made by Mattel Toy Company; no one else had plastic moldling experience ! (At least on the furniture !) The early M16 ammo used the same powder as the 308, NOT a good fit !

  5. I have seen, at 200 yards, 55 grain bullets go sideways through paper targets when fired from a 20 inch barrel with 1:9 twist. From this same barrel (Bushmaster AR-15) hand-loaded 69 grain Sierra Matchkings patterned 1 MOA at 300 yards.
    I use 55 grain for CQB training, and use 62 grain or better for everything else – in fact,n since >70 grain is not manufacturer-recommended for 1:9 – I try to use 69 grain match bullets for everything but short-range blasting (out to 50 meters).

  6. A suggested website: Providing ballistic information, regarding bullet weights. Search: ” Ballistic Coefficients – Sierra Bullets – The Bullet Smiths ”
    Aside from the custom bullet manufacturer: I prefer the Sierra line of bullets, for the following reason – Consistent Bullet Weights. After comparing each individual bullet weights per box, I have found Sierra to be more consistent, than other manufacturers. A variation in bullet weight, can effect the flight path of the bullet. Nosler is another fine choice of consistent bullets. The Sierra Match King is my favorite choice for 30 Cal., Rem. 6mm, and 222. In the 60’s with Viet Nam, the Colt AR-15 was matched with the 223 bullet. The 223 ad the 222 are nearly the same round. Note: Federal Ammunician uses the Sierra line of bullet.
    For the loading enthusiast: Remington brass is a great choice. The price is reasonable and the brass is relatively soft .and easier to work, than other manufactured brass.. Soft brass doesn’t Crack as easy as other brass does. As a result, rimming and turning the necks of Remington Brass is made easy. I later incorporated Lepua brass for the 6mm PPC. It’s a superb product but much more expensive than other products. Not a good choice for either semi of fully auto weapons.

    1. I loaded to ONE single grain of powder variation in my hunting and target range bullets in .270 Rem. in a Remington 700 Shot groups wer always under 1″ at 200 yds. Sierra bullets Only for deer and elk hunting.

      1. The caliber was built around the 130 gr bullet. I always used the Sierra 130 gr boat tail bullets. For Elk the 150 gr and Mother took 6 with the 150 gr bullets from Remington out to 350 yrd’s or more. Model 700 BDL bolt–2 bucks (5 points each) shot less than 3 seconds apart at 185 and 196 yd measured by a Cpl in the Sheriff’s Office with a range finder on a stiff mountain down angle. Bullets placed less than 2″ of the same place on both deer. Mother told him to check the bushes of the first shot; the buck was just out of sight and it spooked the 2nd buck ! Mom was good !

  7. Someone commented on barrel length, above. I have a 1:9 20″ barrel that shoots it’s best with 72 gr. Bergers, 69 gr. Sierras just behind, 75 Hornady’s shoot a pattern, not a group ! But my 1:9 24″ will handle 77’s just fine. Agree that 1:7, 1:8 is best for most(like service rifle shooters) wanting to be able to punch holes close together from 2-600 yds.with a variety of bullet weights. Both 1:7 20″ barrels I’ve had handled 52-80gr with appropriate loads fine- they will shoot better than I can hold. When AR’s first hit service rifle , lots of folks were blowing up 52 gr. Sierra’s through the 1:7 Colt barrels, trying to use ’em for a 200 yard load. I heard that Sierra changed jacket thickness later – I’ve never had one disintegrate, but have “smoked” some home swaged bullets with .22 casings used as jackets(LOT thinner than J4’s !)

  8. How about shooting from a 7.5 ” barrel with a 1:9 twist? Would the lighter load still be favorable? Obviously accuracy wont be great with such a short barrel just looking for advice, thanks.

    1. In regards to Eric P’s question: Was wondering if the barrel is Thompson Center, or Bull Berry? I would suggest contacting Tompson Center, or Bull Berry’s research deparment. Their research department does extensive testing on various combinations of barrel length and twist rates, in respect to various bullet weights. Their testing is exact, in that the conditions are constant. A constant gives you a standard from which to experiment. With this information, one can experiment with various recommended smokeless powders, bullet weights, and the seating depth of the round. If not, one can experiment with a wide range of manufacturers and various types and weights of bullets.

      The weekend shooter, often shares his/her favorite rounds and combinations with friends. What works for one doesn’t necessarily work for another. By using factory recommended specifications, one has a refrence point from which to experiment. One must remember, a factory gun is far more accurate, than nearly all of the better shooters.

      The Tompson Center is a fun weapon to shoot. Consistency is a must, to achieve accuracy with the Thompson. If bags are used, setting the bolt, that holds the fore-end, in the same location on the bag, will improve accuracy. If holding the fore-end with the hand, place the hand on the same fore-end location, with each shot.

      Speaking of barrel length, a 5″ or 7″ barrel isn’t necessarily more or less accurate than a 10″. Human reason has a tendency to choose the 10″ for increased accuracy. The powder charge and bullet weight can increase or decrease the accuracy on either barrel.
      My Aero Engineering experience has been a real asset, in helping me to realiize, just how important consistency is.

  9. Speaking of accuracy: For the shooter that questions the possibility of a single five shot group at 100 yards, the following column would be of interest. Google Search: ” Record Breaking Group: Jim Carmichel Sets Bench Rest World Record / Outdoor Life ” I was recently surprised to see: 6mm PPC competition at 600 yards, with sub 1″ groups.
    There are so many more factors to extreme accuracy shooting, than loading a round into the chamber, and pulling the trigger. Temperature, wind speed and direction, and mirage: are factors that can greately effect ones accuracy. Even
    the depth of the bullet set into the barrel lands is crucial. The single most important factor to accuracy is PATIENCE. Without patience, accuracy is similar to rolling the dice.
    For the AR-15 shooter that wishes to load their own ammo, I would suggest looking into the Dillon line of progressive loading presses. Superb equiptment at a reasonable price. Dillon carries nearly everything the loader requires. Having personally owned Dillon Progressive Presses, I can speak of the quality that goes into each Dillon product.

    1. I’ve had a Dillon 550 since the early 1980’s. My experience with Dillon re after sale support and service, long after sale can only be described as AMAZING.

  10. The ravages of time being what they are, I don’t shoot much of anything these days. That said, I do remember when rifles were 30 caliber, and twist rates were mostly 1 turn in 10, for the 7.62mm NATO, Winchester and the U.S Army seemed drawn to 1 in 12, who knows why. In any event, 1 in 10 twists, as I recall, handled up to 190 grain wt. and 1000 yard ranges in 30-06 quite well, while the 7.62mm NATO with 1 in 12 did quite well out to 600 yards. From my personal experience, at 1000 yards with a .308, I might just as well have been throwing rocks, poorly selected rocks at that. Seems like life was a lot simpler back then, which no doubt clearly shows that I’ve just gotten old, grouchy too.

  11. I have a 1-7 bbl that shoots 55gr, 69and 77 gr very nicely, but 62 gr goes 4″ high and rt…? 16″bbl.. Shooting new PMC fmj bt (XM855). And it shoots 77gr the best with avg 1′ groups

  12. I have wasted a lot of time over the years reading useless articles in various gun magazines typically regarding high priced weaponry that nobody except gun writers can afford to shoot and write about. This article however ranks right near the top for a complete waste of time for both the author and the reader. Has everything about AR-15 already been written that the author had to resort to this type of useless drivel.

  13. I would like to see the same tests done with barrel lengths of 16 and 20 inches. I use an 18 inch barrel with a 1:7 twist rate by Wilson Combat. I have shot only 55 grain but have some 75 grain on order from Black Hills that I’m looking forward to testing.

  14. Mỹ bolt gun (Mossberg) is a 1-9″ with a 24″ barrel. The best group I have gotten so far at 100 yards, was 5 shots in .48″. This was with Australian Outback 69gr. SMK. ammo. Every group with that ammo has been under an inch, while I only have gotten a couple of groups under an inch with 55gr. bullets. I just got some IMI 77gr. ammo, but have not had a chance to go out with it yet

    1. Strangely, not in every case… the same concerns
      Also apply to 1/9 and the 75gr, like the Hornady
      Match .223…. but my Mossberg MVP Patrol 16″
      1/9 shoots it quite well, and it worked in a 18″
      Remington 700 VTR I had. You actually have to try it… results may vary, as they say on commercials

  15. For the serious competition shooter: I would recommend that you contact both: Hart and Shillen barrel manufacturers. Both are manufacturer of AR-15 competition grade barrels, and can provide information regarding twist rates and bullet weights, for a specific length barrel. For the shooter that loads his/her own ammunition, they can recommend a specific powder, number of grains per charge, bullet weight and a recommended custom bullet manufacturer. For my style of shooting, I chose the Colt AR-15 Flat Top, and found it to be quite accurate at 100 yds. Speaking of accuracy, I would suggest that you use a rifle rest and bags, when checking the rifle for accuracy.

    My passion was 100yds & 200 yds 6mm p.p.c.Competition Bench Rest. My rifles were custom built with Hart barrels and Shillen actions. My average 5 round group was .ooo3. At 5 ft it looked like a single hole. I reached that level after two solid years of practice 3 days per week. The rifle was accurate but the shooter needed lots of practice.

      1. He might mean to say C-T-T, center to center. But still, that is hard to believe for sure. Three shots would be spectacular, 5 shots is almost unbelievable.

    1. Paul:

      Re your response concerning M-14’s, M-1’s and the current favorite, you ain’t kidding about this getting old business, they aught to outlaw it. I’ve had limited experience with the M-14, that said, they seemed like a nice rifle, I shot a few matches with them. I had a lot more experience with the Garand in 30-06 persuasion, having fun about 12,000 rounds through one that I owned, it was a Winchester make, of which there were relatively few. I shot National Match Course type competition plus long range, 600 and 1000 yards with mine. I was a whole lot better with the Garand at 600 and 1000 yards than I was shooting off hand at 200. Eventually, I switched to bolt action rifles, mostly Model 70’s, the Standard Target Rifle in both ’06 and .308. I used to get more than a now and then odd look, as I shot left handed, couldn’t see sights with the right eye, so it was shoot south paw or not at all. These days, to,old and or to lazy or both for that game. Shooting matches at military bases was always interesting, especially having contact with Gunnery Sgts. at Quantico, Cherry Point, and Camp LeJeune, sometimes with officers too, people who were rifle shooters. Take care.

      1. At DaNang in the TET Offensive I had occasion to pit 186 rnds thru a M14 in under 4 minutes against over 50 Vietcong; I live, 12 of them did not. The barrel had to be replaced and the action tweaked a good bit. Chrome Moly barrel- Match Grade and other parts the same as match grade. Sure hated to leave that gun behind; at 500 it shot under 3-4″ at rapid fire- USMC rifle range uses. Master Gunnery Sgt was the man that worked the USMC competition team for 15 yrs who worked on my rifle. One chest, one head on 12 of 14 kills and 12-20 more hit.
        Not 20 yrs old anymore sadly.

    2. Paul:
      Re your mention of Hart barrels,once upon a time, I has a Hart SS tube on one of my bolt guns.It shot well, however I didn’t think any better than the Douglas Premium Air Gage Chrome-Molly barrels I usually used. I used to deal with Tim Gardener who was their shop foreman, a gentleman who was kind enough to show me round their shop, in the process answering what might have been my silly questions.Of course, I was not a barrel maker, he was. As to Match Grade Garands, I had once upon a time, put in a request for one, they were going for about $150 at the time.My request was drawn and everything was fine till I noticed the requirement for Social Security Number on the paper work. I wrote back to Col. Smith, at the DCM withdrawing my purchase request, and sent the paper work back to him. I met him subsequently at Camp Perry. We had an interesting conversation. I might have been foolish, can’t say, however some things raised red flags for me, still do, the bureaucratic abuse of Social Security Numbers standing quite high on a list thereof, especially given that there is a most interesting 7 word admonition on my old SS card. Those 7 words. read as follows.For Social Security Purposed Not For Identification, which always struck me as the beginning and the end of the story. Old grouches don’t change except for growing grouchier. Keep your powder dry, primers cool.

  16. I’m finally clear after that excellent lecture on the twists and grains and rpms. Well done. I’m gonna print this for reference.

  17. Well written article. The only thing I feel should have been included is at least a brief explanation of the greenhill formula.

    1. The bullet button was invented to insure a round being chambered on a faulty bolt Carrier group. The Dynamics have been and remain the jepordady of Albert heisnstein. ;,? Whom, Coarsed the Manhattan project. Thanks for our life’s..Eureka.!!
      There’s a buildings ment to detect long range missle in your view as well I meant your watch , I feel to say Denver.
      The Germans. Exiled, .Really ment to rename there buera

  18. ESTE SI ES UN GRAN ARTÍCULO,QUE VA A DAR QUE HABLAR,PERO TAMBIÉN QUE ENTENDER,PARA NO
    COMETER ERRORES,EN DEFINITIVA NO SE PUEDE VULNERAR LA INGENIERÍA,QUE ESTÁ CALCULADA
    CON EXACTITUD

  19. For 35gr in 1:7 test, I believe the expected result is that bullets fragment *as they leave the barrel*, hence the pieces from fragment strikes on your target.

  20. I’ve got a CZ bolt gun in 223/5.56, with a 1:9 twist bbl. I get better groups with 77 gr bullets than with 55 gr and 60 gr bullets. But then again, I have just begun testing my hand loads in this gun.

    1. barrel length will also determine success or Failure i will bet you have a barrel between 24-27 inches…. to make the 77 shoot better than the 55…..

  21. If you will re-read the last paragraph, he pointed out that he had no problems with the mid weight rounds in either of the twist rates. The article was designed to show if there was an observable issue at the extremes of twist and weight. It did a good job of doing that. It was a test of the extremes, not the means.

    1. Thanks for pointing that out. I wasn’t sure at what point a bullet moved into the “too heavy” for the 1:9 twist, but on rereading it shouldn’t make a difference.

  22. I believe my AR’s are 1:9, and I shoot both 55 gr and 62 gr bullets. From your discussion, I assume that I am fine with the 55 gr, but that the heavier 62 gr bullet would be better suited to a 1:7 barrel. Nonetheless, is there any reason not to use the 62 gr bullet, that is, are the differences in performance small to insignificant with a 1:9 barrel?

    I am headed to the range tomorrow, and I will do some comparisons with both bullet weights.

  23. What about the most standard one – 55GR and 62 GR. Most people will not be shooting the very light 35GR or heavy 80GR rounds. Even the military mostly uses 55GR and 62GR.

    You need to do the same test using 55GR and 62GR rounds using both the 1:7 and 1:9 barrels. Again these are the rounds that the majority of Americans will be shooting to include the military.

    I understand what you were putting out to everyone, but you were using weights that most people do not have access to. I thought this article was a waste of time and effort.

    1. Totally agree. I would have found it more valuable to know how the barrels perform with standard off-the-shelf 55/62 gr loads. Since by the author’s own inference, it doesn’t matter what weight the bullet is as the length is more important. Maybe Tom could do another follow-up bang test on some standard ammo for use non-ballistics geeks.

      AND, thanks Tom McHale for another insightful article. I do enjoy the info.

    2. If you go back and read the article he specifically stated why he didn’t use standard 55 gr ammo. There was no point to do such a test with standard ammo as it will work fine in either twist rates and will not display erratic behavior. That’s pretty much what he said. He probably assumed we all knew that so he didn’t elaborate on it.

        1. He also said that he didn’t test with the 55 or 62gr. bullets because in the 1:7 or the 1:9 twist barrels because they will work fine in either load or combination!

    3. I agree, why use the rounds that were not fitted for Semi Auto, all AR’s are Semi Auto.Why the god awful waisted weights? Most of us have better sense than to use that Bullet Combination. What was the true purpose of the article? It had very little if any usable information. This is what we don’t need as information pure BS.

      1. I routinely shot 77 grain through a 20″ h-bar. No, they won’t load from a magazine, I use a sled and single load each round. At distance, the long heavy bullets are extremely accurate. Many hand loaders use this combination. It’s not really pointless just because it’s pointless to you.

    4. As the article stated, 1:7 and 1:9 barrels will shoot those standard loads pretty much identically, so testing them would show nothing. The whole point was to go to extremes to illustrate what happens with over and under twisting situations. And you can very easily get into those situations with standard ammo. The loading at extremes just shows the results more clearly.

      1. Mr. Mc Hale,
        I am a bit long in the tooth now as I approach my 70th year on this earth.
        I got my introduction to the 223 Battle Rifle in the 60’s prior to my service in Vietnam Nam. Sir I must say that from the first round I put down range with that weapon system to this day I never attempted to chamber a round that was ineffective. I am sure you have much more time behind the trigger than I do but loading at extreams makes no sense to me. Just my old ways of evaluating the performance of my weapons.

        1. The bullet button was invented to insure a round being chambered on a faulty bolt Carrier group. The Dynamics have been and remain the jepordady of Albert heisnstein. ;,? Whom, Coarsed the Manhattan project. Thanks for our life’s..Eureka.!!

  24. I sure would like to see a bullet work down on powders ESPECIALLY THE 336,OOO RPM MODEL. subsonic would be a cook part 2 on the barrel twists information. Great Article. If I wasn’t opening up a new Gun Store I’d be there helping. I am always giving this kind of information out to reloaders. In the store we free reloading on dillion 1050, 650, 900 and rcbs single stage, and lee. I show people basics and advanced technology. This is Great stuff.now you gave me the reloader flu again.

    1. @Michael A. Sharpe Where are you located? I wish there were more places like you that showed “newbies” how to reload for free or gave advice for free. Most places I know of either do not show people how to reload due to liability insurance reasons or they charge an arm and a leg to do so. I have a Lee Breech lock Challenger kit, Lee reloading manual, Lee .270 win dies, and I doo not have a place to set it up! LOL my nephew and his family moved into the basement along with almost all of their stuff. I cannot set up in the garage because there is no room there either. I know I have to get some more equipment and a couple more manuals before I start to reload/load any ammo.

  25. You know what they say – “There’s no such thing as pure B.S. It’s always contaminated with a little fact!” Thanks for a great article. I enjoyed it.

    1. This is what I think:
      The original M-16 was designed to shoot a 55 Gr. FMJ, and had a twist of 1:12. This “marginally” stabilized the projectile, which would tumble on impact, as the 174 Gr. Mk VII .303 British did.
      When the eggheads tried to make the M-16 into something it never was designed to be — a 400 meter-plus round. By making it shoot heavier and heavier projectiles, the twist had to be increased.
      As a result, the M-16 became more accurate, but less lethal. Which is why I think that both the AK round, 7.62X39 mm, and the 7.62 NATO, are both far better than the .223.

      1. Actually, the attempt was to make it more lethal. The light weight 55 grain bullet, as should be obvious, wasn’t exactly a man stopper.

        Shooting competition for the Army, the 55 grain was accurate well out to 55 yards.

        1. I’d read that the intent for going from the .30-06 to the .223 was to make a less lethal round, to cause more injuries that would create more drain on manpower to get a wounded soldier to safety. A wounded soldier might require a couple guys to get him to safety as well as cause more detrimental psychological effect to the other soldier who’d hear and see the amount of pain he had. A dead soldier is in no hurry to leave the battlefield and doesn’t make any noises, so he doesn’t occupy additional manpower to evacuate during a firefight. Considering that, it sounds like accuracy would have been the main reason behind the heavier bullet rather than lethalness.

          1. In 65 they were telling us less weight of both rifle and ammo. Therefore we could carry more ammo. And believe it or don’t the increased velocity would cause wounds such as a shot to the hand would create so much shock it would break all the bones in that arm!!

          2. @riochet007 Everything after your first comma is true, but applicable to the 5.56 coming out of a 1 in 12 twist barrel.

        2. Actually, I have used the 55gr 1/12 M-16A1 in combat, and out to 250m, It is brutal as to what it does to the human body… It is a fair round out to 325m….. and accurate to 550m but then you are hitting with about the same velocity as a .22 LR, 1,000fps and 110 fp, As you point out, They tried to make it into something it was never intended to be a 700 meter gun…..

          My own build for a EOTWSHTF EDC is a 1/12 twist, and a lot of 55 gr. in a 16 in mid length gas, Carbine, I still start the bullet over 3,000fps, and have within 5% Plus or Minus the same terminals ballistic out to 300m, Which will cover 99% if any situation……. There isn’t many points in my AO that require 300+m range, and for those that do, I have a .375 mag and a fine selection of soft and full bullets to handle some hard targets.

      2. @Al Whitney, True, Stoner was wise enough to use the 1 in 12 twist to make a barely stable bullet that tended to tumble when it hit something in the human body, thus getting around the clean survivable wounds requirement of the Hague Conventions. Infantry men loved it. Army REMF bureaucrats ruined it.

        1. 1/14 was the original twist rate, and the was the twist on the model 01 purchased by the USAF, and the Project Agile guns sent to Vietnam
          With the early Special Advisors.
          1/12 was adopted after the Artic tests were conducted in Alaska.
          Accuracy suffers in -40degree dense
          Cold air . So because the M16 was to deployed all over the world, 1/12 was adopted. But as far as horrid wounds with M193, 1/14 was king
          As reports from project Agile bore witness to.

      3. The original twist was 1 in 14..it was the twist of the rifles originally sent to Vietnam and responsible for the glowing reports of the ‘explosive’ hits. When the Army redesigned the M16 to the A1 series it changed the twist to 1 in 12 to stabilize the tracer round – the same reason in the 80s when the twist rate of the A2 series was changed from 1 in 9 to 1 in 7….to stabilize the tracer round, both of which are slightly longer than the standard 55 and 62 grain bullets…

    2. There was some good info for people new to ARs and reloading. Myself, I would be more interested in seeing if there is any real difference in a 1:8 barrel and a 1:7 shooting the 80 grain bullets.

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