Edit: I posted the opposite of reality, so I had to erase it.

 

Heavier= longer=faster twist to stabilize.

 

Not just heavier, Hybrids too. IIRC Berger VLDs talk about 1 in 8". I'd have to go downstairs to check.

 

Wow. I guess I typed too early in the morning. I posted the EXACT OPPOSITE of how twist rates work! Ha!

Thank you @6/250/40 for clearing that up.

 

Short answer with a broad brush stroke: It depends, it matters, but not a lot, and not as much on pistols as it does on rifles....so don't sweat over it.


Just for discussion sake-

There is a window of mass, dimensions, distribution of mass, muzzle velocity, and twist rate that will provide a window of accpetable performance. Start busting those factors, and you start having problems as any precision rifle shooter can tell you. It is the same thing here with pistols, just on a smaller "Scale" if you will. The initial kinetic input of angular momentum (velocity vs twist rate) is what puts the spin(rpm) on, and the stability is a result of that input on the bullet construction. (mass, distribution of mass, and dimensions).

The primary reason many production 9mm pistols went to a 1:10 twist from a 1:16-18 and slower was to provide additional stability when passing through barriers at an angle and to get the bullets to do what they wanted in gel. A 1:14-18 twist is generally more accurate than 1:10, depending on the bullet weight and velocity, on account of precession. The best accuracy I have found at distance on 9mm comes from 124gr at +p type velocities on a 1:16 twist, but other combinations have shown good results in testing I have seen. This is why certain army units modify their Glocks to 1:16 barrels and run things like Speer gold dot 124 +p. Additionally, (again broad brush stroke) a faster twist will result in less penetration and more JHP expansion, which helps 9mm in meeting gel testing requirements, as mentioned above. Lighter bullets require more gyroscopic stability to pass through barriers more cleanly than heavier ones. From what I have gathered from 45ACP bullseye shooters, the 1:16 doesn't seem to give anything up on faster twist rates, and I haven't seen angular deflection issues in barrier testing. The mass and distribution of the 45 at the velocities used doesn't seem to be as impacted by this as 9mm is, despite what the math may say. I personally don't mess with handgun twists outside of 1:10-1:16, but you could probably find a bullseye shooter home brewing specific handholds for that specific purpose that would.

Keep in mind you've got to get pretty far into the weeds on angles and distance for this stuff to start to show, much less be exploited or matter. For the most part, you're going to be fine if you stick with traditional 9mm twists in the 1:10-1:16 range, across a broad range of projectile types. If you're planning on shooting out past 50m regularly, then a twist rate slower than 1:10 will serve your purposes better. If you're just talking about your every day carry gun for every day carry gun purposes, it doesn't really matter.

But again, this is all splitting hairs. Circles are a 10 round group shot at 100m from a G34.5 with a 1:10 twist barrel and a 147gr projectile. It will group tighter with a 135 +p, and would group tighter still with a 1:14 barrel, or by going to a 124 and a 1:14-1:16. The vertical dispersion up into the 8 was error on my part.

Hope that helps.

 

Here's a table I put together a while back looking at the RPM's of bullets at various rifling twists, using SAAMI standard bullet weights and velocities. I do not know the bullet lengths. A 1:10" rifling twist is the normal twist for a 9mm. If you are new to this, it is saying that the bullet makes one revolution for 10 inches of linear travel. A 1:16" twist is normal for a 45.

We know that at a bullet gets longer for the bore size, the faster it must spin to stabilize. This is more apparent in rifles as the rifle bullets are much longer for the bore size than what we see in handguns. This is very evident with the 5.56mm cartridge. As the bullets have gotten longer (heavier) the rifling twist rate has been increased. I believe the military is presently using a 1:7" twist rate.

Schumann was the first barrel maker that I'm aware of that offered barrels with barrel twists as slow as 1:32". Wil Schumann sold his company some time back and I have no contact information for him to permit asking him the advantages of the slower twist rates. Thus my inquiry here, to see what I can learn with respect to why someone would want, say a 1:24" twist for their 9mm instead of the standard 1:10" twist rate.

Bullet​	Bullet​	Twist Rate​	Twist Rate​	Twist Rate​	Twist Rate​	Twist Rate​	Twist Rate​
Weight​	Velocity​	10​	12​	14​	16​	20​	32​
grains​	fps​	in/rev​	in/rev​	in/rev​	in/rev​	in/rev​	in/rev​
88​	1,500​	108,000​	90,000​	77,143​	67,500​	54,000​	33,750​
95​	1,330​	95,760​	79,800​	68,400​	59,850​	47,880​	29,925​
100​	1,200​	86,400​	72,000​	61,714​	54,000​	43,200​	27,000​
115​	1,135​	81,720​	68,100​	58,371​	51,075​	40,860​	25,538​
115​	1,210​	87,120​	72,600​	62,229​	54,450​	43,560​	27,225​
124​	1,090​	78,480​	65,400​	56,057​	49,050​	39,240​	24,525​
124​	1,120​	80,640​	67,200​	57,600​	50,400​	40,320​	25,200​
135​	1,060​	76,320​	63,600​	54,514​	47,700​	38,160​	23,850​
147​	985​	70,920​	59,100​	50,657​	44,325​	35,460​	22,163​

 

the change to being 1:10 hasnt always been the norm, and Id argue it isnt fully the norm still. Staccato, for example, still uses a 1:16, others do too.

twist rates in the mil 5.56 going to 1:7 were based on getting the m885 through the barriers (armor) it was designed to deal with. The 1:8 is actually more accurate even at 77gr, and the 1:9 more still up to a certain weight.

The chart above is rpm based on mv and twist rate, but stability is a formula of angular speed and mass. in general, your most accurate barrel for a given application will be the one that has the slowest twist and still stabilize the given projectile. higher bullet rpm doesnt automatically mean more accurate.

It's a balance between what you need the bullet to do in flight and what you need the bullet to do when it hits the intended target, and twist rate impacts both.

 

Yes, the chart lists RPM's only. Stability is a different prospect. Spinning a bullet too fast will magnify any imperfections. This leads to, as you state, the slowest twist that will stabilize.

I had understood the military 1:7" came from the tracers at artic conditions.

I'm stating the 1:10" as the norm due to it being given by SAAMI for the 9mm Luger. It's not binding for a manufacturer, but the pressure test barrels will have it.

I'll look more at the stability factor.

 

When I loaded the Hornady HAP bullets years ago I read about people using 1:32 twist for the 115gr. HAP specifically and I thought that I maybe screwed up and bought the wrong bullets, but I never had an issue in my 9mm's that had 1:14 or 1:16 twists. I have never been a good enough shot to notice a difference between twist rates on a 9mm but I have never owned a 1:24 or 1:32 twist 9mm. Around the time that I read about 1:32 twists for 115gr. HAP's, I read something about the 1:24 twist being "best" for the 9mm but no one uses a 1:24 twist as far as I know.

Twist rate having an effect on JHP performance and deflection makes sense. From an accuracy perspective, some of the twist rate stuff I have seen from Bullseye/accuracy shooters about the 9mm doesn't make sense. My DW PM9 has a 1:16 barrel and it's the most accurate centerfire I own. I can't imagine what that gun would do in a Ransom Rest.

From what I've seen, a 1:24 or 1:32 barrel on a 9mm is for something like a Bullseye gun that will see one specific load with one bullet "optimized" for the twist rate for accuracy. Is there truth to that? Are there other applications for the 1:32? I get twists in the teens, but 1:32? That is a drastic difference.

 

There is not a change TO a 9mm 10 twist, that was what ol Georg and DWM started out with, anything else is a change FROM the 10 twist.

C.E. Harris had Barsto make him several barrels for a BHP. All at 16 twist but will different chambers. Then he added on one made out of a .38 Special blank with 18.75" twist and .358" groove. It was the most accurate.

Schueman made barrels with 32 twist for light bullets at high velocity. If you wanted something Special, he had a gain twist option. I don't recall the starting twist, but the exit twist was 24".

Swiss Sigs had a lead bullet barrel option. I finally found out that it had a 20 twist instead of the usual 10.

Jerry Keefer liked fast twist barrels to stabilize low velocity bullets in midrange target ammo. He made some 10 twist barrels for 1911 and M52.

 

There is not a change TO a 9mm 10 twist, that was what ol Georg and DWM started out with, anything else is a change FROM the 10 twist.

C.E. Harris had Barsto make him several barrels for a BHP. All at 16 twist but will different chambers. Then he added on one made out of a .38 Special blank with 18.75" twist and .358" groove. It was the most accurate.

Schueman made barrels with 32 twist for light bullets at high velocity. If you wanted something Special, he had a gain twist option. I don't recall the starting twist, but the exit twist was 24".

Swiss Sigs had a lead bullet barrel option. I finally found out that it had a 20 twist instead of the usual 10.

Jerry Keefer liked fast twist barrels to stabilize low velocity bullets in midrange target ammo. He made some 10 twist barrels for 1911 and M52.

its a fair point. I guess it depends on what you use as your starting point in time. There was a period of time during the transition from revolvers to semi auto duty guns that twist rates relaxed for accuracy, but then sped back up for barrier and expansion performance.

1:10 isn't the best for accuracy over distance for most commercial loadings, but does better through barriers. Obviously hand loading to different velocities can affect accuracy of different twists too.

 

How is the torque value determined? The slower twist rates, having a smaller rifling angle, should show less torque.

 

Tryibg to look at the torque, come up with;

45 at 850 fps with a 1"16" twist, torque = 6.03 ft-lbs

a 9mm at 1100 fps and a 1:10" twist gives 12.654 ft-lbs (850fps , 4.5" barrel)

These are, of course, very brief with bore times of 0.000441 sec for the 45 and 0.000348 sec for the 9mm (1100 fps, 4.6" barrel)

 

🤔

I'm pretty far outside my expertise here, but....

That torque shouldn't matter much to the unlock time, it seems to me. Unless there's a lot of friction between the barrel and the locking lugs. So the more highly polished (i.e. higher end customs in particular) your interfaces are, the less it should matter. Or so I theorize.

As I say, I'm driving past my headlights even making a comment in this thread 😂

 

I don't feel the torque does anything regarding the unlock (ramp down) function of the gun. It does have to do with how the gun feels/acts in recoil, trying to twist the gun in the hand. As with recoil in general, some people are more sensitive than others.

When I first posted, my goal was to explore the possible effects to the shooter regarding torque with the varying rifling twists. Slower rifling twist translates to less torque, as I see it, whether or not I can put reall numbers to it.

 

@Buccaneer12, I’m curious about a few comments you’ve made here which seem to indicate better “accuracy at distance” with slower twist rates. Could you expand as to why?

I am of the impression that there is a min and max twist rate for a particular situation (load, barrel length, etc.) and that we should expect differences across the range. But within the “known good” range I would expect more gyroscopic stabilization from a faster twist to result in better accuracy and precision due to an evening out of forces as it were.

On the other hand, I do understand that slower twist will result in higher velocity which, as long as it has enough stabilization, will have a positive impact to accuracy and precision due to flatness of trajectory, time in flight, wind, etc. Perhaps this is what you meant by increased accuracy over distance?

 

@Buccaneer12, I’m curious about a few comments you’ve made here which seem to indicate better “accuracy at distance” with slower twist rates. Could you expand as to why?

I am of the impression that there is a min and max twist rate for a particular situation (load, barrel length, etc.) and that we should expect differences across the range. But within the “known good” range I would expect more gyroscopic stabilization from a faster twist to result in better accuracy and precision due to an evening out of forces as it were.

On the other hand, I do understand that slower twist will result in higher velocity which, as long as it has enough stabilization, will have a positive impact to accuracy and precision due to flatness of trajectory, time in flight, wind, etc. Perhaps this is what you meant by increased accuracy over distance?

it has to do with precession and orbiting. Broadly, a tighter twist rate does not automatically result in tighter accuracy. Generally, the slowest twist that stabilizes the particular bullet at the particular velocity produces the tightest accuracy, but will impact stability through barriers. Velocity will affect the drop and drift, but its a negligible delta in pistols.

It's worth noting that a 45 bullet its bigger and heavier than a 9mm, and at slower velocity. By conventional wisdom, it should require more twist, not less, than 9mm. But most 45's Im aware of run 1:16, not 1:10. On the surface, that seems contradictory.

again, this is speaking of commercial and gov spec ammunition. Im sure experienced bullseye shooters making specific hand loads have their own requirements and findings. And again, inside of 100m, or super light bullets or at an angle, its really splitting hairs and i dont want to give the impression this is a bigger deal than it is for most applications. The convo with everyone is fun, but esoteric.

good posts by Jim et al.

 

That torque shouldn't matter much to the unlock time, it seems to me.

I don't feel the torque does anything regarding the unlock (ramp down) function of the gun.

Well, here is what Randy Lee has to say about that. Page 8, post 75 & ff at

https://pistol-forum.com/showthread.php?8390-Apex-Barsto-barrel-M-amp-P-9mm/page8

I do try to not make stuff up. You may debate the details with Mr Lee.


"The resitance due to the increased torque forces imparted to the barrel by the bullet in the M&P helps to prolong the dwell time. Think of it as trying to twist and pull on the barrel while firing the pistol. The faster twist increases the rotational forces on the barrel which, in a sense binds the barrel in the slide for a slightly longer period of time. The slower the twist, the less binding effect. It is a minimal gain, however our test results at 50 yards between factory 1:18.75, 1:10, a 1:16 and our 1:10 show statistical relevance to the idea."

"By increasing the torque forces on the barrel (increasing the twist rate), the factory was hoping to use this binding effect to improve accuracy. In some cases it does- however when all the manufacturing tolerances are at the extreme ends of the spectrum, you will find pistols that are minute of barn door accuracy.

Our barrel was designed to use the torque imparted by the faster twist rate to enhance but not rely on it for barrel stability. The chamber end of the barrel maintains vertical stability by resting on the horizontal surface of the locking block. Our muzzle end is at maximum diameter, so that the front end remains locked against the slide bore with maximum surface contact. When we fit the barrel, pulling back on the slide even so far as .100" and perform the muzzle test, you will find that it remains locked until the locking block pulls the barrel down for extraction.

The enhanced stability at both ends of the barrel are why our barrels typically shoot around 1" at 25 yards (2"@50) with good quality ammo regardless of bullet weight."

 

Well, here is what Randy Lee has to say about that. Page 8, post 75 & ff at

https://pistol-forum.com/showthread.php?8390-Apex-Barsto-barrel-M-amp-P-9mm/page8

I do try to not make stuff up. You may debate the details with Mr Lee.


"The resitance due to the increased torque forces imparted to the barrel by the bullet in the M&P helps to prolong the dwell time. Think of it as trying to twist and pull on the barrel while firing the pistol. The faster twist increases the rotational forces on the barrel which, in a sense binds the barrel in the slide for a slightly longer period of time. The slower the twist, the less binding effect. It is a minimal gain, however our test results at 50 yards between factory 1:18.75, 1:10, a 1:16 and our 1:10 show statistical relevance to the idea."

"By increasing the torque forces on the barrel (increasing the twist rate), the factory was hoping to use this binding effect to improve accuracy. In some cases it does- however when all the manufacturing tolerances are at the extreme ends of the spectrum, you will find pistols that are minute of barn door accuracy.

Our barrel was designed to use the torque imparted by the faster twist rate to enhance but not rely on it for barrel stability. The chamber end of the barrel maintains vertical stability by resting on the horizontal surface of the locking block. Our muzzle end is at maximum diameter, so that the front end remains locked against the slide bore with maximum surface contact. When we fit the barrel, pulling back on the slide even so far as .100" and perform the muzzle test, you will find that it remains locked until the locking block pulls the barrel down for extraction.

The enhanced stability at both ends of the barrel are why our barrels typically shoot around 1" at 25 yards (2"@50) with good quality ammo regardless of bullet weight."

the issue i take with this is that he is comparing a fitted barrel to a non fitted barrel. Barrel fitment and barrel tolerances, at least as best as I can tell, matters more than twist rate, especially since he is talking about fitting both the lugs and the tube.

Torque from barrel twist is something Ive never heard discussed as a factor that matters on pistols. Could be that it does, and Its just beyond my basis of knowledge/experience, but I struggle to see how it matters. The bullet clears the crown before unlocking occurs, and the initial kinetic moment of torque applied by the twist can impact the bullet itself but is a minuscule amount on the gun itself. It is possible based on a couple of his comments that the issue he is addressing is specific to the M&P, but Im not familiar enough with the platform to have an opinion. It isnt clear to me how a fitted barrel with correct lock up requires different tq values from a barrel twist to make a difference, but again, I dont know much about the M&P. Id have to see the data to understand or believe it, because it contradicts everything Ive seen. My guess is he uses a 1:10 twist because thats what the company white labeling his barrels offered him. The regardless of bullet weight part is a bit of an eye brow raiser for me.

The BA barrel in my long range instructor gun is still a 1:10 twist, but the tolerances are something absurd like .0001. It is absurdly consistent. But, had that barrel been made with a slightly slower twist rate, the gun would pattern tighter, and we've seen that in testing time and time again with kkm 1:16 and the wilson fitted 1:16 on 124 nato rounds.

some of this matters on bullet weight and velocity, too. My 1:10 twist will beat a factory barrel with 1:10 twist with any bullet weight. A fitted 1:16 will generally beat a factory 1:10 twist with any bullet weight. A fitted 1:16 on 124 will beat my 1:10, a 147gr might affect the results.

hang loaders of specific weight, design, and velocity have their own findings. Im speaking in terms of commercial ammunition.

It's also splitting hairs. If you arent bullseye shooting or trying to go out beyond 100m, i dont think it matters functionally. Just get a good fitted barrel.

Just my $.02

 

What advantages, or disadvantages, do you feel a slower twist rate gives?

Thanks for your comments and insights.

I have seen great results with fast twist 45 barrels using low velocity target loads. I have a high master shooter running a 1/10 Krieger with lead and could not be happier. I have a lot of information forthcoming on this topic.

KKM makes a 1/32 twist barrel. It can only shoot a 115 grain bullet at high velocity but it is unbelievably accurate. Shoot any other bullet out of it and the accuracy falls off a cliff.

I agree with @Buccaneer12 on the topic. 16 is a great all-around twist rate for both 9 and 45. The only reason to go faster or slower is to specialize for Bullseye or some other shooting discipline.

 

Its another good point. Reducing velocity and upping the twist or lessening the twist and increasing velocity will make alterations to the rpm and the effect of the initial kinetic moment by the twist.

if we think about a string pulled top, the effective "twist" is always the same. But the harder you pull the cord the faster the top spins. Pull it too fast and youll see the top orbit around the center line before settling in. Bullets can do the same thing.

as far as combat engagement with a pistol goes, we typically set 1.5" @ 25m as the floor for the Glocks so it stays at 6" or better at 100m with an 80% hit factor at 200m. The BA, KKM, and Jarvis barrels ive tested have all hit this. There was a period of time where some of the Glocks had their frames heated so that the frame rails could be widened and true'd, then polished, and then the slide rails crushed after hand fitting a barrel. Those guns typically saw 1.5" @ 50m from a ransom rest. This is all based on 124 nato and 124 +p gold dot. changes to weight or velocity varies all this.

would be interested to hear more of what data you have.

 

Georg Luger originally used a 1-10" twist rate when he designed the cartridge in 1900..

 

There are people using 1-14" twist in .45 for lighter bullets with great results.
Most factory twist rates are pretty arbitrary. The last manufacturer I worked with on barrels initially used 1-16" for all .355 barrels because that was the industry standard for decades but eventually moved to 1-10" for better accuracy results with 147gr bullets.

Oddly enough, the trend in the precision pistol (Bullseye) world, at least in 9mm, is 1-32" twist and that will only work well with a 115grain bullet.

 

Oddly enough, the trend in the precision pistol (Bullseye) world, at least in 9mm, is 1-32" twist and that will only work well with a 115grain bullet.

Very odd since Jerry Keefer had it figured out in 2004. 9mm long slide, Kart barrel, 25 shots out of a ransom rest at 50 yards with low velocity AMI Match ammo 147 gr XTP Hornady

 

The Randy Lee comments are spot on. The M&P suffered from an early unlock issue and a faster twist can certainly help that. Most semi auto pistols rely on the friction of the bullet to push the barrel forward (in lockup) while the gun is firing as a reaction to the case that is attempting to push the slide open..

The gun fires, barrel is pulling forward by the drag of the bullet in the rifling, and the slide is pushed to the rear by the case head bearing against it and the expanding gases between. The slide not allowing the case to budge pulls the barrel back approximately .100"± as the bullet exits, and link down begins. During this phase while the bullet is in the barrel the links position has changed from in extension to compression and back to extension, this in .100" of slide/barrel movement, no foul, as the barrel's position wasn't changed relative to the frame.

If you doubt the frictional forces here, try to push a bullet from the chamber end of the barrel through the bore with a cleaning rod. It's near impossible.

 

Friction is the primary cause of the barrel hgeating when shooting. The exposure to the hot powder gases is so brief there is no real heat transfer. But friction, lots of heat produced.

 

Guys what a fantastic thread. I started another thread trying to understand why my Stacatto won’t shoot and sometimes keyhole 147 grain hollow point training ammo flying under 1,000 fps.
I guess that bullet at that twist has caused me much pain and suffering. Bucconeer12 thank you.
PB

 

Guys what a fantastic thread. I started another thread trying to understand why my Stacatto won’t shoot and sometimes keyhole 147 grain hollow point training ammo flying under 1,000 fps.
I guess that bullet at that twist has caused me much pain and suffering. Bucconeer12 thank you.
PB

im surprised youre having issues with 147 from a staccato. The 1:16 should be fine for it to stabilize unless the velocity is super low. Id call them up

 

That Geog Luge rused a 1:10" for the original 9mm may have been a carry-over from the 30 Luger that used the 1:10" twist. Just my speculation.

 

Perhaps ask Mr Harris about determining the torque on the bullet as it's rotated by the rifling?

Thanks.

 

Yes it does on some bullets. Cheap Winchester white box 115 JHPs are garbage in a 1 in 10 twist.

 

I had this question a while back when I saw Springfield Armory used a 1:10 twist in their non-1911 9mm's but used a 1:16 twist in their 1911';s

It seems that their pistols with a 1:10 twist are made overseas (Europe) where that is standard ( actually 1 : 9.84 in or 1: 25cm ) The 1911's that are made in Genesco, IL have a 1:16 twist as do most domestically made 1911's.

 

In rifles the twist is more important and with the advent of Hybrids the bullet makers are very specific about twist rates. Refer to Berger VLD bullets.

Not just heavier, Hybrids too. IIRC Berger VLDs talk about 1 in 8". I'd have to go downstairs to check.

This isn't accurate.

using Berger 308 as an example: The Berger VLD and the Juggernaut under 200grains will hit stability factors over 1.5 at velocities of even as low as 2500fps in twists of something like 1:11. The big factors that play into a bullet's stability are velocity and length. You don't need to go down below 1:10 until you hit north of 200gr. The benefits of faster twist rates play out in both energy deposited on target, bullet expansion, and the big one: stability through transsonic. This is why the new M110SASS A1 is running a 1:8 twist barrel while still running M118LR, and the results through transsonic speak for themselves. Bullet RPM falls off at a slower rate that velocity does, as you well know, but the higher RPM out of the gate gives a better BC later in the trajectory. The moral of this story is that you can spin a modern bullet faster than was previously believed, and usually without a loss of "tactical practical" accuracy.

Monolithics sometimes buck the trend because they can both handle a higher RPM with less precession and in some cases require the higher twist based on their length because of the solid construction.

This is moot, however, because we're talking about pistols, not rifles.

In pistols, what we have seen the most (at least, so far) is that the faster twist barrels (specifically in 9mm) allow generally better performance through intermediate barriers with less deflection (ie off angle through windshield glass), and generally more reliable expansion depending on the construction of the bullet. Interestingly enough, 45acp exhibits much less deflection at the same 1:16 twist rate of "slower" twist 9mm. My presumption is that the mass of the round is leading to a higher gyroscopic stability at the same twist rate, but it's speculation on my part.

So far, the 1:14 twist and 1:16 twist in the majority of 9mm loadings seems to be showing the best accuracy results for 124 and 147gr rounds. I'll be really curious to see the information from our colleague @mbacker_99 here that is conducting a large series of tests on this. It's the first test of its kind that I am personally aware of. I'm looking forward to learning on this one.

 

Id love to weigh in, but im far from having any modicum of ballistics knowledge, esp compared to say, a guy like @Buccaneer12. So I wont pretend that I do.

 

Tao of Bullshido 2 (c) (ii) (b)- Humble not yourself when lacking knowledge. Name drop instead....