Finding The Correct Barrel Twist Rate
BY Herschel Smith2 years, 1 month ago
The rate of the rifling twist inside a rifle barrel would seem to be mostly a gun thing as opposed to an ammunition thing. However, for ammunition to shoot accurately, the bullet must be stabilized, and for a bullet to be stabilized, the rifling rate-of-twist must be compatible with the bullet’s length and velocity. This means that twist rate is very important to ammunition, and it is why the Sporting Arms and Ammunition Manufacturers’ Institute (SAAMI) establishes standards for twist rates as they relate to arms and ammunition.
This is a good thing. It’s why when you purchase ammunition for your firearm, you can expect that ammunition to shoot at least reasonably well. Most ammunition manufacturers make ammunition to SAAMI specifications, which means the bullets—at their launch velocity—will mesh well with the rifling-twist rate of the gun for which you bought them. It can, however, be a bad thing, as history has shown.
In 1955, Remington introduced the .244 Rem. cartridge. It fired a .244-caliber bullet and had a stipulated rifling-twist rate of one turn in 12 inches (1:12). The cartridge worked great with bullets in the 55- to 90-grain weight range. However, that same year Winchester introduced the .243 Win. (I’m betting Winchester had a spy inside Remington.) The .243 Win. also fired a .244-caliber bullet, but Winchester very wisely specified a 1:10-inch twist rate for the rifling. This meant Winchester’s 6 mm cartridge could handle heavier—longer—bullets of 100 grains. Both cartridges became popular, but the .243 Win. won the battle even though it was not quite as fast as the .244. Why? Twist rate. Eight years later Remington tried to save its .244 by reintroducing it as the 6 mm Rem. and tightening the twist rate from 1:12- to 1:9-inch. This allowed the cartridge to better compete with the .243 Win. But, it was too late.
Remington has always seemed a bit late to the game.
Almost the exact same thing happened to Remington again in 2008. That’s the year Hornady introduced the 6.5 Creedmoor, which fired a .264-caliber bullet out of a cartridge case similar in size to the .260 Rem. Remington had introduced the .260 in 1997 and it had become a very popular cartridge for long-range target shooting and hunting. However, Remington stipulated a 1:9-inch twist rate for the .260, while Hornady stipulated a 1:8-inch twist for the Creedmoor. Because of the Creedmoor’s ability to handle longer, more aerodynamic bullets, Remington got twisted out of the conversation again.
I’m not really sure that’s completely why – I think free bore had something to do with it too, maybe a lot more things. The folks at Hornady don’t appear to like free bore at all and want the bullet as close to the leade as possible, just at the rifling, in order to avoid bullet deformation. That’s one reason they don’t like the 300 Win Mag (stock ammo, not reloaders) and do like their own 300 PRC.
While all this was going on, developments with what is now the most popular rifle cartridge in America were struggling through another twisted situation. In 1964, the .223 Rem.—yep, here we go with Remington yet again—was introduced. It was initially famous as the cartridge of the AR-15 and, in 5.56×45 mm form (which isn’t identical) as the cartridge of the military’s M16. The .223 Rem. had a specified twist rate of 1:12 inches, which was about perfect for a 55-grain bullet at 3,200 fps.
But, in the early 1980s, the 5.56 NATO cartridge was standardized. Externally, the cartridge-case dimensions of the .223 Rem. and the 5.56 NATO are identical, but the chambers are different, and the 5.56 NATO is loaded to higher pressures. Also, it is a military cartridge for which there are no SAAMI specifications. Initially standardized with a 62-grain bullet, 5.56 NATO rifles have a much faster 1:7-inch twist rate. This allowed the 5.56 NATO to stabilize longer bullets that were heavier and shot flatter. Aficionados of the .223 Rem. caught on and started re-barreling .223 Rem. rifles with faster-twist barrels and loading their own ammo to take advantage of newer and longer bullets.
However, most ammunition for the .223 Rem. is still built to work with the original 1:12-inch twist rate. Why? Well, there are many, many thousands of .223 Rem. rifles out there with a 1:12-inch twist. If you have one of those and purchased ammo loaded with a bullet that needs a 1:8-inch twist, you’ll struggle to hit a snuff can at 100 yards. But, some ammo makers are now offering .223 Rem. ammo that needs the faster twist.
Rifle manufacturers are doing the same. For example, Savage initially used the slower twist rate for the .223 Rem., but by 1995 all Savage 110 rifles in .223 Rem. had a 1:9-inch twist. In 2007, Savage added a 1:7-inch-twist-rate barrel to several models, but when it entered the AR-15 market in 2017, the company settled on the 1:8-inch twist for its MSRs in .223 Rem. or 5.56 NATO.
Of course, factory .223 ammo designed for a 1:12-inch twist will shoot just fine in the faster 1:8- or 1:7-inch twist barrels and in 5.56 NATO rifles. (Do not shoot 5.56 NATO ammo in rifles chambered for the .223 Rem.) This is one of the reasons many modern AR-15-style rifles are chambered for the 5.56 NATO instead of the .223 Rem., and it’s also why many manufacturers now load 5.56 NATO ammo and sell it commercially. Some manufacturers also cut .223-caliber chambers to the .223 Wylde chamber to allow for the firing of both .223 Rem. and 5.56 NATO ammunition—more accurately in the case of .223 Rem. and safely in the case of 5.56 NATO.
Cartridge designers have now finally learned and are specifying fast twist rates when new cartridges are introduced. Just look at the 22 Nosler, 224 Valkyrie, 6 mm ARC, .277 SIG Fury; the list goes on. Today, longer, more aerodynamic bullets pushed through fast-twist barrels shoot flatter and hit harder at distance.
Tim Harmsen at Military Arms Channel did a video of an M-16 shooting in a 1:12 twist gun into ballistics gel, and other media, and it seemed to outperform the shorter barrels with tighter twist.
Anyway, it’s ironic that this discussion occurred the next day after we touched on these issues. Also, in my AR-15 category there is a lot of discussion on ballistics and twist rate. I won’t recapitulate it here.
Take all of this for what it’s worth. He speaks it as gospel, and I suspect not much of it is.
I will remark that I very much like the performance of the 6mm ARC. It’s a pure pleasure to shoot, without recoil noticeably stronger than the 5.56 and yet with vastly superior results.
On September 13, 2022 at 10:42 pm, Andy said:
I wish the Us army would have pursued the 6mm Arc for the NGSW. I haven’t personally shot it, but would like to try it out in the AR platform.
On September 14, 2022 at 1:25 am, Georgiaboy61 said:
@ Herschel Smith
Re: “Tim Harmsen at Military Arms Channel did a video of an M-16 shooting in a 1:12 twist gun into ballistics gel, and other media, and it seemed to outperform the shorter barrels with tighter twist.”
Eugene Stoner, then chief engineer at Armalite Corporation, and James Sullivan downsized the AR10 to fit the RFP (request for proposal) issued by U.S. Army CONARC commanding officer (1956-1958) General Willard Wyman in his “Small Caliber High-Velocity Rifle” project. Wyman bypassed the Army Ordnance Dept. which was opposed to small-caliber weapons at that time, and used Infantry Board funding instead to get the project off the ground.
It stipulated a light-weight rifle firing a .22-caliber cartridge using a 55-grain bullet at 3,300 fps, having lethality equivalent to or superior to the M-1 Carbine, in a rifle weighing 6 pounds, and capable of penetrating a steel helmet at 500 yards, which was also specified as the maximum effective range of the weapon.
Stoner and his team faced a steep challenge in these requirements, which were – to put it lightly – a tall order almost seventy years ago. But Stoner had an ace up his sleeve, technically-speaking, namely, the exterior ballistic characteristics of small-caliber, high-velocity bullets in flight. Specifically, their propensity to become unstable and yaw more-quickly (all else being equal) than heavier bullets of larger caliber.
Stoner’s team needed to produce lethality on par with the .30 Carbine round, which at 110-grains was double the mass of the 55-grain projectile being considered, and of .30-caliber diameter.
Normally, for the civilian hunting market, the answer to making a small high-velocity bullet more-lethal against prey animals is to design an expanding or hollow-point bullet, but since the U.S. government is party to the Hague and Geneva Conventions governing land warfare, those options were off the table as these treaties prohibit them.
To solve this technical hurdle, Stoner instead exploited the “fleet yaw” characteristics of the lightweight high-velocity 55-grain bullet, i.e., its propensity to tumble (“swap ends”) and fragment inside tissue. By designing the 55-grain FMJ bullet to fragment at impact velocities at/above around 2650-2700 fps, multiple wound channels were created, effectively mimicking the tissue damage caused by HP/expanding rounds, without actually being designed in that manner.
This work-around, which was true to the letter of the Geneva and Hague Conventions, if perhaps not the spirit, met the requirements set forth by General Wyman and the new high-velocity small-caliber rifle project was off-and-running.
Eugene Stoner and his team originally specified a 1:14 twist 20-inch barrel on the earliest AR15s trialed by the U.S. military, but when there were reports of inconsistent cold weather performance from the 1:14 barrel, the twist rate was modified to 1:12, which is what the first M-16 rifles to go into combat in SE Asia had as their twist rate.
As the war continued and more troops, Army and Marine alike, began transitioning to the new assault rifle from the older M-14, reports of the effectiveness in combat of the new rifle and its cartridge began to make their way back to the rear and spread from there within the armed forces.
Some troops reported almost horrifying effectiveness out of the new weapon, which was said to cause lethal wounds all out of proportion to the small size of the cartridge. Other troops complained of inconsistent performance and watching enemy “tangos” absorb multiple center-mass hits without sustaining incapacitating wounds, particularly at more extended ranges.
These inconsistencies were taking place alongside the now well-known teething troubles experienced by the new weapon upon its introduction to large-scale use in SE Asia, due to changes in ammunition formulation not approved by Stoner and other factors.
At the time, the brass and civilian specialists in the Pentagon/DOD did not know what to make of these reports, but since Sec-Def Robert McNamara was behind the new rifle, most of the complaints were quietly ignored. Senior commanders in the field and their SNCOs tended to blame the men themselves for these problems, but the grunts were having none of it and were fighting mad that they and their buddies were paying the price in blood for the botched introduction of the rifle.
Ultimately, complaints reached relatives at home and then elected Congressional representatives in Washington, D.C. An outcry ensued, which resulted in the Ichord Hearings of 1967, named for Congressman Richard Ichord of Missouri.
Stoner’s original design was extremely-effective using M193 55-grain FMJ/Ball from a 20-inch 1:12 twist barrel. This combination imparted the correct degree of stability to allow the projectile to perform as intended by its designers.
M193 was “hyper-lethal” at MV of 2700 fps or above, which was sufficient to reliably producing fragmentation/shattering of the projectile, but this lethality dropped somewhat as MV fell at increased range. The M16A1 was highly-effective inside 200 yards, with acceptable effectiveness out to 500 yards. The reader will note that these performance parameters align closely with those attained by the prototypical assault rifles of the WWII & post-war period, namely the German MP43/StG44 (7.92×33) and the Russian AKM/AK47 (7.62×39).
Shorter barrels mean lesser effective range using Ball/FMJ ammo, at least if the soldier or Marine is using M193 55-grain or M855/SS109 62-grain ammunition.
This tradeoff was seen as acceptable for troops needing compact weapons for special operations, operations from aircraft or vehicles, etc.
Since Stoner’s design is so dependent upon high MV for its performance when using the military-issue ammunition of that era, it should not be surprising that effectiveness dropped off considerably once barrels got too short. This is probably the reason the Army and Marines did not go shorter than 14.5-inches in their standard-issue carbines, again except for unique uses and special-ops personnel.
After reading the complex history of the AR15/M-16, the arm-chair historian might be tempted to ask whether the system performed as intended or not. Well, one answer comes from our Cold War adversaries, the Russians, who – when it came time to modernize their AK47 – decided to reconfigure it using a round whose performance was very similar to Vietnam-era M193 Ball/FMJ, namely the 5.45×39 cartridge. Imitation is the sincerest form of flattery, yes??
Short-barreled ARs are all the range these days, whether in the military or out of it…. but don’t hesitate to buck the trend if you prefer the 20-inch tube. That’s how Eugene Stoner designed it and that’s still how it works best, especially if you plan to shoot 55- or 62-grain loads from it.
On September 14, 2022 at 8:24 am, RHT447 said:
Interesting read–
http://www.jouster2.com/Sagaof16Part1.html
On September 14, 2022 at 1:06 pm, Georgiaboy61 said:
@ RHT447
Interesting read indeed…. thanks for posting it. If it is germane, I know a half-dozen or so men who are combat veterans of Vietnam, a mix of Marines, soldiers and one Navy FMF Corpsman. They are somewhat older than I am – as I was too young to go to SE Asia (turned fourteen in 1975). Small sample size, obviously, but at a party years ago, we talked about Vietnam and you should have heard those guys! They didn’t have a single good thing to say about the M-16, and if you have ever heard a grunt cuss and complain, you know how memorable that can be!
But yeah, they hated the “black rifle,” which they called a lot of unprintable things I won’t repeat here. So along comes the son of the one of the hosts, the guest of honor at the BBQ/party – an Army 11B just back from Iraq. We button-holed him, handed him an adult beverage and asked his views. He said that he liked his issue weapon, an M16A2, just fine – and that it had never let him down.
Anyway, that’s my one story dating to that time and the men who used them in Vietnam.
On September 14, 2022 at 2:28 pm, RHT447 said:
@ Georgiaboy61, 1:06 pm
My pleasure. There is a lot of good stuff on that site, and free to download too. Here is one example–
http://www.jouster2.com/sea_stories/end_of_an_era.pdf
My own experience is in the same lane as your story. In 1975 I was in the middle of my Army hitch, stationed just outside Nürnberg. My MOS was Small Arms Repair, and I was in a maintenance company. I did not serve in Vietnam, but along side many who did. Those vets were just about unanimous in their disgust with the M16’s they were issued.
In the early 90’s, I got my FFL and proceeded to make a local name for myself building custom AR’s, in California, no less. Wife and I escaped Kalifornia for Texas in 2015. My last build was for myself after we got here. The AR platform has come a long way. Not surprised the young guest of honor liked his.
On September 14, 2022 at 4:57 pm, Georgiaboy61 said:
@ RHT447
Re: “The AR platform has come a long way. Not surprised the young guest of honor liked his.”
If you built custom ARs, then you the story of “The Mouse That Roared,” the tale of how the “black rifle” conquered not just battlefields, but competitions such as the Camp Perry National Matches. Glenn Zydiker, I believe, is the man’s name who penned the book… competitive shooter of some renown.
As much as old-school guys like me and the fathers/grand-fathers of my generation love and venerate Garands, M-14s, Springfield M1903s and other wood-and-steel firearms of yore, a properly tuned AR15 with match-grade ammo and a good man behind the rifle will out-shoot almost any service rifle you can name. That’s how the “mouse gun” ended up topping those older designs.
Stoner’s design is inherently accurate for any number of reasons, but you already knew that, I am sure…. thanks for writing….
On September 14, 2022 at 8:38 pm, RHT447 said:
@ Georgiaboy61, 4:57 pm
Glen Zediker, indeed. He wrote several books including the one you mention. I was saddened to hear of his passing. I am familiar with his work through his website (now sadly gone too). I referred many folks there over the years. He was extremely generous with his time and talent, posting a small library of articles, all downloadable for free. His game was NRA Highpower, as was mine. I got my Master card in 1990.
I am also an old school die hard fan of rifles made from wood and steel, like God intended. I got my Garand from the (then) DCM back around 1981. At the end of each rifle match season, I would shoot it in the last match. Yeah, my score would drop, but I didn’t care. I just love shooting that old rifle. “Ping!”
On September 15, 2022 at 12:06 am, Georgiaboy61 said:
@ RHT447
Re: “I did not serve in Vietnam, but along side many who did. Those vets were just about unanimous in their disgust with the M16’s they were issued.”
The villain in that particular saga, in my opinion as a historian, was Secretary of Defense Robert S. McNamara (1916-2009) if it was anyone. McNamara had served in the armed forces in WWII – USAAF if memory serves – and then became a big-shot executive with Ford Motor Company. Mac was an authority on systems analysis and he and his “Whiz Kids” as they were termed, believed wholeheartedly in scientific management, with their reams of computer printouts and slide-rules, and so on.
There’s nothing wrong with using high-tech tools and statistical and other forms of analysis in your work, provided it is done appropriately and isn’t taken to extremes. The problem with Mac and his Whiz Kids is that they refused to listen to anyone who wasn’t a “true believer” in their methods.
They considered themselves experts, when in reality, most of them were out of their depth working in the defense sector in the first place. Arrogance and ignorance are a dangerous combination.
Men who’d spent their entire lives in uniform mastering the profession of arms were being overruled by wet-noses with slide rules and mainframe printouts. Men who had spent their entire adult lives designing and manufacturing arms, and so on.
McNamara committed at least two – maybe three – cardinal sins, vis-a-vis his handling of the service rifle issue, during his tenure as Sec-Def, which then cascaded into a whole raft of second- and third-order effects.
Whatever the merits of the M-14 service rifle – and I happen to believe it was/is an excellent design in many respects but that’s neither here nor there – by 1961-1962 or so, it was well-established as the primary long arm of the Army and Marine Corps, and the initial kinks and problems in production had largely been worked out. Rifles were coming off assembly lines at Springfield Armory, TRW and other vendors/manufacturers and being issued to troops in the field and on duty around the world.
In short, production and use were going reasonably smoothly, and the rifles were working as intended in combat and in the field, apart from the usual sorts of minor and easily-correctable problems which accompany the manufacture and use of any new military arm.
McNamara and company got wind of the new lightweight AR15 assault rifle – and based upon favorable reports from General Curtis LeMay and the USAF (a service which never adopted the M-14) and also U.S. Army Special Forces already in theater in SE Asia -decided to put it into production.
Normally, this would not necessarily be a problem, even though that meant that there were then not one but two standard issue rifles… but McNamara decided upon the switch from the M-14 pretty much unilaterally and without adequate consultation with the various service chiefs and other authorities and stakeholders, and worse yet, he did it before the AR15/M-16 was ready to be put into the field and into combat as a standard issue weapon, and in the midst of an escalating war in a very challenging operational environment.
New weapons have been introduced in the midst of hot on-going wars, it is true – but the stakes have to be very high indeed in order to justify the risks associated with pushing a new and still-largely unproven weapon into the hands of the troops when a more-proven and still effective option is available. Vietnam wasn’t WWII; there should have been no haste or undue rush whatsoever to get the new weapon into action… but McNamara and company did it anyway…
and we now know the disastrous results.
McNamara then compounded the problem, making it much worse by arbitrarily shutting down M-14 production around the same time, circa 1963, Just as it was ramping up and putting these effective and reliable weapons into the hands of the men who needed them, not just in SE Asia but in Europe and around the world.
When the introduction of the weapon into the Vietnam conflict did not go as smoothly as predicted, rather than investigate reports of problems on an honest and upfront basis, the Pentagon brass and DOD blamed the troops in the field for problems with the new rifles. Men were dying in combat with jammed and disassembled M-16s at their feet, while McNamara and his Whiz Kids preened about how splendid a job they were doing. A fiasco which ultimately led to the Ichord Hearings in 1967 and a considerable scandal surrounding the issue.
McNamara’s handling of the conflict was very ill-considered and disastrous in many other ways, which I won’t consider here, but a final parting shot proved yet again how myopic and unwise he was: McNamara closed the national armory system down entirely in 1968, just before leaving office as Sec-Def. A system of armories and ordnance specialists which had served the nation – and largely well – since being established by George Washington, our nation’s first president.
McNamara cited some problems with cronyism and corruption and overall inefficiency as the reasons for his decision, but none of that really holds up under examination. Yes, there had been some problems with cronyism and corruption, but it isn’t as if these things are confined to government organizations; they are equally common in the civilian defense sector.
Moreover, McNamara – while making much of the alleged weaknesses and detriments of the national armory system, unfairly declined to consider their strengths and the positive attributes they offered to the nation: Namely, an organization in place which collected ordnance, small arms and manufacturing experts under one roof. The institutional memory and knowledge alone which was lost by this foolhardy and ill-considered decision was arguably priceless. But the guy just flushed it all down the toilet.
I am not against private industry generally or against the defense industry specifically; rather, I am disgusted by the way in which the guy threw away years upon years of accumulated knowledge, wisdom and expertise more or less on a whim.
On September 15, 2022 at 8:40 am, RHT447 said:
@ Georgiaboy61, 12:06 am
Concur, and thanks for the history lesson. I am going to copy and save it. I did not know that McNamara shut down the national armory system. IMO, he was a vain, egotistical, yes-man, just the sort that LBJ (spit) wanted working for him.
For those readers who may not know–
Here is a heartbreaking video about McNamara sending low IQ troops to Vietnam–
https://www.youtube.com/watch?v=_J2VwFDV4-g
When Kelly Johnson tried to develop the SR-71 Blackbird to the next level, McNamara said no, claiming cost. Not to be denied, Johnson made a pitch to the Joint Chiefs. All the production jigs were owned by the government, so McNamara had them destroyed.
On September 15, 2022 at 12:08 pm, Georgiaboy61 said:
@ RHT447
Re: “Concur, and thanks for the history lesson. I am going to copy and save it. I did not know that McNamara shut down the national armory system.”
I had forgotten about McNamara’s cynical and immoral program to induct low-IQ men into the military, for the purpose of sending them to Vietnam. What a Charlie Foxtrot that must have been! That endangers not only the poor guy himself, but all of the men in his unit. Contrary to popular opinion, soldiering is not an activity for the mentally-deficient. It takes brains and good judgment to do well (insert GI humor here, LOL)
I had also forgotten about his criminally-negligent handling of the SR-71 situation. Destroying the jigs, fixtures and tooling for one of the greatest aircraft ever built – which rightfully belonged to the American taxpayer – was hubris run out of control.
Apropos of that comment, Kelly Johnson was a brilliant man and a visionary. If you have not read “Skunkworks,” by Ben Rich & Leo Janos, consider doing so. Rich was one of Johnson’s proteges, I guess you’d call him, who was there for much of that era.
Thanks for the history lesson in return; always good to learn new things or be reminded of old things which needed refreshing.