9mm Barrel Twist Thoughts/Questions

I'm not a professional gunsmith.  But I enjoy both shooting and tinkering with guns.  Over the years I have built a half-dozen or so wadguns that were accurate, reliable, and had fairly decent triggers.  Since I have a small machine shop I have also built a number of jigs and special tools that facilitate some of the jobs, such as barrel fitting and trigger work.  I've concentrated on accuracy and feel especially gratified when a gun I have built shows good accuracy.  Recently I have been considering playing with 9mm on the 1911 platform; not so much as a bullseye centerfire gun but just to see if I can build an accurate one.  Along that line I have had some thoughts and done some calculations (I'm an engineer but not a ballistician) on 9mm barrels.  Anyone is welcome to chime in here, but I'd especially welcome the thoughts of Jerry, K.C. and others who have struggled with the 9mm accuracy problem.

My starting point is the famously accurate 38 Special 148gr HBWC round out of the really good PPC guns, which pretty much all seem to use barrel twists of 10-12".  The Remington Targetmaster 148gr round runs about 770 fps, and out of a barrel with 12" twist is spinning 46,200 rpm at the muzzle.  Since that round is so accurate, my thought is that the 147gr 9mm bullet, which is only .002" smaller in diameter than the 38, should also be accurate if spun at the same rate.  Unfortunately, to get the 147gr bullet up to that rotation using common 16" twist 9mm barrels requires a muzzle velocity of about 1026 fps, which is nearing a maximum load and certainly would not qualify as low recoil. Essentially, my thought is that if we had match quality 9mm barrels with a twist of 10-12", we could push something like the 147gr XTP at a speed of only 750-800 fps with the fast spin (46,000+rpm) needed for accuracy, and yet have a relatively soft recoil.  In fact the 147gr 9mm bullet and the 148gr 38 bullet pushed at the same speed would have essentially the same "calculated" recoil impulse.  I know the "felt recoil" would be different because the case capacities are different, but they would be close.

At the risk of damaging my own argument, I will note that I am aware that some of the most accurate 9mm ball guns are using the KKM 32" twist 9mm barrel and a 115 grain bullet.  Even at a blazing 1200 fps that barrel is only spinning the bullet 27,000 rpm, which I guess must be enough to stabilize that short bullet.  But frankly I am puzzled that the slow twist works so well on even the short 115gr bullet.

What do you 9mm 'smiths think?  Am I off track here?

Not a 'smith but KC is building a pair of 9MM 1911's with the KKM 32 twist barrel for a shooting buddy and myself as I type this.

- Dave

I don't know if this applies to pistols but this is from an article I book marked from AccurateShooter for rifle loading/barrel selection:
http://www.accurateshooter.com/technical-articles/calculating-bullet-rpm-spin-rates-stability/

"It is generally believed that, for match bullets, best accuracy is achieved at the minimal spin rates that will fully stabilize the particular bullet at the distances where the bullet must perform. That’s why short-range 6PPC benchrest shooters use relatively slow twist rates, such as 1:14″, to stabilize their short, flatbase bullets. They could use “fast” twist rates such as 1:8″, but this delivers more bullet RPM than necessary. Match results have demonstrated conclusively that the slower twist rates produce better accuracy with these bullets."

Dr. Don;
I  love topics and thinkers like you..
I am working on a .38 CF BE gun at this moment.. Numerous PPC guns in prior years. So I have a fondness for the .38 148 gr HBWC. I think you either made a typo, or found some wrong info on the FPS of the Rem Target Master.. It's closer to 710, as nearly all factory 148 match ammo is.. It's a sweet spot for that round. Many of us shot reloaded ammo that was running in the high 600s FPS and shot record scores and many cleans..  Back in the early 80s 1X10 twist was king of the heavy revolvers. Later, Shilen would only make it special order. They stated that 14 twist was universal and everything else was special order.. Douglas held out with the 10 twist.. I used a lot of 12 twist toward the end of the PPC days. The best groups I ever got were 12 twist..But I would take a 10 twist without worry..I have seen 10 - 12 - 14  twists all shoot into an inch, and some less than an inch out of very good guns.. Now that was with closely fit brass gas rings, Taylor Throats, indicated 2 axis crowns, and full contact barrel threads. So it takes a lot of small things to make it  happen along with twist.. I don't care what you do to a factory 18.750 twist barrel.. It will never shoot with the faster twist barrels..
I have always disliked the 9mm for anything, but as you say, the projectiles are essentially identical.
In 2001 the team Capt. of the Richmond PD team stated he would do me harm if I didn't build them PPC 9mms. Not only did they win, but those guns set a National record that held for 10 years.. Always want to do better right.?? They wanted to switch to 1-32 twist, because, that's what everyone else was shooting. Fads .. Switched back to the old 16 twist barrels a few months later..So I concur with your suspicions about slow twist.. It reminds me of a saying way back in my drag racing days.."Heavy flywheels are for Tuna boats." / "Slow Twist is for muzzle loaders.."
For twist rate, it's always better to err on the side of speed..I recently made a  1X14 twist 1911 45. Shot a ..700 diameter barrel tester group..with factory Zero.. Hmmm..
Next I want to try a 12 twist for lead..  I like your approach.. The machine fitting of the guns is now so good, that the last frontier is the barrel.. It hasn't changed in 100 years..Same twist, same land to groove ratio.. I think there's more to be gained..
Sooo, to get a faster twist than 16 in the 9mm, you'll have to sleeve or make it from scratch.. I'd make it from scratch..

Gain twist is coming back to rifles. Remembering that some of the old Cap and Ball revolvers used it, I wonder if it might offer anything for bullseye. Granted you don't have to worry about your bullet disintegrating from over spinning at 400 yards, but a gradual spin up from the lead might offer some improved performance. Or maybe not.

Reminds me of the tale told to me by Forest Davis of while he was a USAF gunsmith building guns for the USAF pistol team using greasegun barrels.  He said that the machine gun barrels were rifled with a twist in the opposite direction!      I think Forest retired from the AF in the late 50s.   He was in the USAF shop at Lackland AFB, San Antonio when Bob Day was there.

Jerry,

Thanks for the encouragement.  I stand corrected on the velocity of the Rem Target Master...I was working from memory there.  While the 710 fps changes my numbers a bit, it doesn't change the argument for a faster twist 9mm barrel.  And your experiences bear that out.  I'm afraid that making a barrel from scratch may be beyond my skill level and is definitely beyond my current equipment.  But I might well try sleeving one if I can find the appropriate barrel stock to turn into a sleeve.  Suggestions are welcome.

Dr.Don wrote:Jerry,

Thanks for the encouragement.  I stand corrected on the velocity of the Rem Target Master...I was working from memory there.  While the 710 fps changes my numbers a bit, it doesn't change the argument for a faster twist 9mm barrel.  And your experiences bear that out.  I'm afraid that making a barrel from scratch may be beyond my skill level and is definitely beyond my current equipment.  But I might well try sleeving one if I can find the appropriate barrel stock to turn into a sleeve.  Suggestions are welcome.

I have a piece of Douglas  1-12 twist in 9mm.. It's the end of the pull, so several inches is not great, but you could chamber that end.. The rest looks great.  I'll never do another 9mm,  you're welcome to it..

jmdavis wrote:Gain twist , I wonder if it might offer anything for bullseye.

I don't  like naming names, but there are a few gain twist barrels in BE... They are not yet setting the world afire...I personally don't think gain twist will ever be a factor.. Now that Precision Shooting Magazine has stopped it's publication, I am some what behind on the trends... Kreiger and Bartlein are usually at the top of the list of winning barrels for rifles...
Kreiger once made a 12 twist .38 for me that was one of the greatest shooting blanks I ever had..

Bartlein is making a gain twist with the amu chamber for the 90gr. It appears to handle 77's and also give good results with the 90's in a service rifle length. A couple of Army Reserve shooters ran them this year at Perry.

They seemed to work pretty well. For across the course.

Jerry, I sent you a PM.

jmdavis wrote:Bartlein is making a gain twist with the amu chamber for the 90gr. It appears to handle 77's and also give good results with the 90's in a service rifle length. A couple of Army Reserve shooters ran them this year at Perry.

They seemed to work pretty well. For across the course.

Did the AMU run them , also..??

S&W claims " The model 952 is the most accurate 9mm in the world". Those are their words not mine. That is a very bold statement. I wonder what they settled on for the twist rate. I have tried to find it in print but all I have found is an article on how they make them in the custom shop (past tense) and that they put a custom twist in the barrel. I can eyeball mine but that is pretty far from accurate.

I know Jerry is strong on the barrel as the last frontier in accuracy but I think there is an element of barrel-bullet interface in there that has to work too. If we weren't just working with what barrel blanks we can get, how would we make them to be ideal? Not just what twist but what proportion of land to groove area and what number of grooves? How deep would the grooves be for lead and for jacketed or compromised to shoot either? What bullet design would be optimal? A scaled down H&G 68 or is there something that would knock it out of the park that hasn't been tried yet?

Jerry Keefer wrote:

jmdavis wrote:Bartlein is making a gain twist with the amu chamber for the 90gr. It appears to handle 77's and also give good results with the 90's in a service rifle length. A couple of Army Reserve shooters ran them this year at Perry.

They seemed to work pretty well. For across the course.

Did the AMU run them , also..??

Not as far as I know. And I would need to master my 1-7 before I thought about a gain twist of 1/12-1/7. The jury is still out on exactly what you gain at 600 (if anything) but they do appear to be working without the problems of the past in the 20 inch service rifle barrel. 

OK enough rifle talk. Sorry for the hijack.

There is an excellent article in the November 2014 issue of Rifle magazine that deals specifically with determining proper barrel twist for any given caliber. There is also mentioned a website where you can input the various factors such as bullet weight, muzzle velocity, etc. and the formula will immediately give you the correct twist.

The web site is http://kwk.us/twist.html. 

Try it out.

Interestingly, I saw some Glock barrels on Midway that are listed as 9.84" twist.  That is 1 turn in 250mm, or the metric conversion of essentially a 10" twist.  They are all too short to use as sleeving options, but it's interesting that they chose the faster twist.  Of course, being Glock, I expect they are polygonal, and that's a whole different world.

Hmmmm, I'm fighting with a SIG P226 and a 10-twist barrel that just doesn't seem to like 115-gr FMJs in the 1,000-1200 range and even down to 973 fps.

JHPs are doing better most of the time, but sometimes not by much. Noslers give me hope more often than Hornady XTPs, which is a surprise. Since they first came out, the 115-gr XTP has been very accurate for me in 9mm, though that was always in stock guns. Now I'm also trying to accurize the thing.

So in the thread where I shared these results, there's a suggestion that I try heavier bullets to see if the groups get smaller.

Nice idea, but I cannot find 147-gr bullets for years now, and the biggest batch of 124 FMJs around these parts is still on the shelf because they are priced at $25/100!

In stock at Powder Valley

HOR35580

HORNADY 9MM .355 147 GR HP/XTP (100)

Yes

$17.71

HOR35597B500

HORNADY 9MM .355 147 GR FMJ-RN (500)

Yes

$69.00

http://www.powdervalleyinc.com/

Not sure these from Penn are in stock but very interesting
http://www.pennbullets.com/9mm/9mm-caliber.html

- Dave

I am playing with 9mm loads for the new S&W 929 revolver 6.5" barrel (Walther?) 1/10 twist. Best jacketed load so far 5.2 Autocomp 115 Zero #135 bullet, Win and Federal primers 1.095 aol 1115 fps 3.5" at 50 yards. Winchester factory 147 tcmc 937 fps also 3.5" . 160 gn SNS cast .38 super win primers 1.15 oal 775 fps 2.5" 

Thinking about looking at a 1/32 barrel for the 929

Tom

9146gt,

Your results with the 160 gr at 775 fps are interesting out of that fast twist barrel.  My hypothetical in the opening post is that a long/heavy bullet like the 147 (or your 160) shot slowly out of a fast twist barrel ought to be accurate like the 38 Special 148 is accurate out of the fast twist barrels.  Love to see you try a 147 or your 160 loaded down to about 675-700 fps.

Jerry Keefer sent me a piece of Douglas 9mm 12 twist barrel and I am using it to sleeve an existing 9mm barrel to get the faster twist.  It will take me a while to get the pistol finished and testable, but I plan to report on it here.

Dr. Don,
why all the interest in making a 147 shoot? I've never heard of bad accuracy concerning the 147 in the standard 16 twist 9mm barrels. The discussion has talked about weight comparisons but it's not just about weight when it comes to bullet stability and accuracy. An important factor in stability is bearing surface and it's ratio to the weight. My Zero 148g hollow base bullet has a rough bearing surface of .625" and my Zero 147 9mm shows a rough value of .325". These are vastly different bullet designs even though they are one grain different in weight and therefore don't need the same rpm or twist rate. This would also account for why 115 hollow points shoot well in faster 16 twist barrels, since there is no weight in the nose there must be more weight in a longer body.
I believe there was much research done in this area and there is a Miller formula for stability (although I believe it was for naval ordnance), I didn't consult it for this post but it can be found through a search engine and might shed light here, it might work against my points! But you didn't mention it in your reasoning.
Don't get me wrong, I am all for your experiment but I just don't understand the basis for it since i've never heard of bad 147gr. 9mm accuracy in 16 twist barrels. Do you have examples of bad accuracy with 147's?

robert84010,
My interest in this was predicated on the general difficulty people have had over the years in building 9mm 1911's with bullseye accuracy levels.  i know it is done, but my impression is that most of the 9mm activity has been focused on EIC hardball guns, and therefore on the 115-124 gr hardball ammo.  I may be wrong, but my impression is that those who have tried 9mm as a potential centerfire candidate have been mostly disappointed.  On the other hand, the 38 Special shooting a slow (700fps) 148 wadcutter has been a great accuracy success in both BE centerfire and PPC.  The PPC guys have experimented widely with this cartridge and found that the faster twist barrels (10-12 twist) are in general the most accurate.  Hence my thinking that a 1911 in 9mm pushing a 147gr bullet at slow speed (675-700 fps) and spun from a 10-12 twist barrel might achieve both high accuracy and low recoil.  The only way I know to get a fast twist 1911 barrel in 9mm affordably is to make one.  Hence the sleeving experiment.

I realize the 148 wadcutter and the various 147 9mm bullets like the XTP are very different aerodynamically and in weight distribution.  That may kill the success of the project. But I thought it was worth the effort so far.

Dr. Don, there has actually been quite good sucess using a 9mm as a CF gun.  The bullet of choice is the Hornady 115 XTP.  Guns have averaged at 1.00 or less.  I'm currently building 2 more.  Just a bit limiting in the ammo it likes to shoot well at 50 yards.

I can only go by my experience but my friend does my gunsmithing and when he built my 9mm 1911 with the KKM slowtwist he said it was the most accurate pistol he ever built and was hoping I would back out of the deal! He ended up building one for himself....

He said the only problem was tuning it to work 100% with a bomar rib on it but the accuracy was there in spades.

A bought a Smith & Wesson 929 9 mm 1/10 twist with a 6.5" barrel to use in Metallic division for NRA Bianchi Cup. It testing so far it likes 160gn .356 38 super projectiles at 775 FPS at 124000 power factor (must be 120000 minimum). Power factor is projectile weight x FPS measured 10' from the muzzle. I would like to keep FPS about 950>1000 as to keep your sight picture on the target for the Moving Target event.

115 and 147 gn jacketed ammo so far is not as good as the lead load. Is there a different land and groove dimensions for jacketed projectiles? This gun hates Atlanta Arms 115 gn match ammo which shoots great in my 1/32 twist 1911.


Tom