Slow twist 9mm barrels

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Slow twist 9mm barrels

Post by Mac2 on 3/14/2016, 11:21 am

It appears to have become conventional wisdom for bullseye to desire slow twist 9mm barrels shooting relatively short bullets.  Have a one turn in 32 inches 9mm 1911 being crafted by KC Crawford as Christmas (or sooner) present for wife.  If possible, I would like to buy a barrel for Springfield RO 9mm (or my old G34) that has slow twist so as to be able to test ammo.  KKM fabricates such barrels - however their WEB site is silent as far as I can see about twist.  The other fabricators that seem to exist include:  Kart; Storm Lake; Nowlin; Nighthawk Custom; and Bar-Sto.  However, all that I have been able to find are suggestions that the slowest twist available is 1:16.

Q-one:  Who, other than KKM, fabricates slower than 1:16 twist 9mm barrels?

Q-two:  Army's AMU apparently did testing of slower twist 9mm barrels.   Where one can find a technical report of their work?

Simulations suggest that HAP 115 at something like 25,000 rpm is just comfortably stable (1:32 twist).  A somewhat faster twist might achieve similar rpm with a lighter powder charge and thus lighter recoil - important for some of us at 25 yards.    Thanks,    Mac

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Re: Slow twist 9mm barrels

Post by james r chapman on 3/14/2016, 1:05 pm

Does anyone know what bbl twist Bob Marvel used in his 1911 ppc 9mm's he has targets posted for on his website?
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Re: Slow twist 9mm barrels

Post by Jon Eulette on 3/14/2016, 1:29 pm

I believe those were Kart barrels. They shoot well! But those bullets are driven fast to do it!
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Re: Slow twist 9mm barrels

Post by Jerry Keefer on 3/14/2016, 1:48 pm

james r chapman wrote:Does anyone know what bbl twist Bob Marvel used in his 1911 ppc 9mm's he has targets posted for on his website?
In 2004, one of the RPD shooters won a 9mm at the PPC Nationals, built and donated by Bob.. It has a Bar Sto 16 twist..The test targets, which I still have, are all 115 gr projectiles from various bullet makers.. The groups range from smallest .950 to largest 1.120.... all the loads were Power pistol @ 6.1 grains..   10 shot/10 group average is .965
The officer is still competing, and I service the gun when needed.. It is an excellent gun..
I have seen numerous 9mm slow twist groups put up by David Sams that are also fantastic..using KKM slow twists..
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Re: Slow twist 9mm barrels

Post by james r chapman on 3/14/2016, 2:27 pm

Thanks both of you. Apparently there is life in the 1:16's.
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Re: Slow twist 9mm barrels

Post by Jerry Keefer on 3/14/2016, 6:13 pm

This has been hanging on my wall for 12 years.. Hence the grubby appearance.. Les Baer frame and long slide with a Kart 16 twist. 50 yards/25 shots/AMI 147 grain.
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Re: Slow twist 9mm barrels

Post by rreid on 3/14/2016, 7:46 pm

Didn't the slow twist barrels come about because of the CMP/DCM requirement that 9mm Berettas use a 115-124gr round nose FMJ?
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Re: Slow twist 9mm barrels

Post by Bigtrout on 3/16/2016, 7:58 am

Jerry, was that group from a Ransom rest?  What an incredible 25-shot group that is!!!
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Re: Slow twist 9mm barrels

Post by Jerry Keefer on 3/16/2016, 8:56 am

Bigtrout wrote:Jerry, was that group from a Ransom rest?  What an incredible 25-shot group that is!!!
Yes, that was RR..
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Still working on finding slow pitch 9MM barrels

Post by Mac2 on 3/20/2016, 4:00 pm

Have yet to find a review of KKM barrels that mentions pitch.  Nothing found on KKM WEB site about pitch.  It is possible that pitch comes up in the checkout process.  Sure was concerned about pitch with precision rifle shooting.  Perhaps the inherent lack of precision with a handgun negates optimizing pitch.
Still looking.  Mac

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Re: Slow twist 9mm barrels

Post by robert84010 on 3/22/2016, 9:02 pm

Mac,
i've been told and I suppose your website hunting confirms that you have to call him up and ask for the 1:32 twist barrels. Tell him you shoot NRA bullseye and you should have no problems getting one. My gunsmith has been to his shop several times and used a 1:32 in my 1911. My Beretta has a Kart and I have complete confidence in both barrels.

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Re: Slow twist 9mm barrels

Post by Jon Eulette on 3/22/2016, 9:36 pm

Mac2 wrote: Perhaps the inherent lack of precision with a handgun negates optimizing pitch.
Still looking.  Mac
I would beg to differ on the inherent pistol accuracy. Have gotten sub 1" groups at 50 with both 9 & 45 over the years. Sub 1.5" is the norm!   Smile
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Ah, the telephone & Inherent

Post by Mac2 on 3/22/2016, 10:23 pm

Tomorrow - at long last - I have no scheduled activities, so it is time for me to use that old fashion instrument of communication that I avoid since E-mail became the new modern.  Seriously, good advice.  Thanks.

No doubt when one affixes a pistol in a RR, and finds ammo that the pistol likes, one can achieve near rifle performance (perhaps 2 or 3 MOA).  I was not careful enough with the wording in my statement.  You are right to call me on it.  I could have hypothecated that few humans, shooting a pistol using one hand, are likely to be good enough that optimizing pitch will enhance their performance.  Put another way: the improvement in performance in moving from a quality 1 in 16 inches to a quality 1 in 32 inches (optimizing ammo along the way) objectively will not be seen as worth the cost and fuss to most - except for an engineer who has been obsessed with precision since a child. 

An additional factor is that in Bullseye we are interested in performance at distances not usually involved with many pistol shooters.  7 yard or perhaps 10 yard performance is their compass.  At such distances, the effect of pitch is expected not to be measurable.

With a rifle, one can achieve sub MOA to a great distance.  A MOA at 50 yards is about 0.5 inches.  Conclusions are left for the student.

My urge to experiment would be tempered if the (supposed) work on 9mm pitch performed by AMU were to be found.  I wrote them a request, but have heard nothing.   Thanks for contributing,   Mac

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Up-date re slower twist 9mm

Post by Mac2 on 4/8/2016, 1:02 pm

Received 1 turn in 32 inches 9mm barrel from KKM with ramp appropriate for 9mm Range Officer (RO).  Will have the new barrel fitted such that old barrel can still be used.  Old bushing seems to have the same clearance on both barrels.  Big apparent difference - not yet fully analyzed - is that the chamber on the KKM seems to be something like 2 mm shorter when I drop in a dummy. 

The good people I spoke with at KKM - using the old means for telephonic communication - made clear that their "standard" barrels use one turn in 18 inches.  I am working on a pair of G34MOS (to use in Unlimited) and have a very old G34 so I also received a 1/18 barrel for G34 - almost half the twist rate of Glock's barrel.  Still too cold for outdoor testing.  [Mounted Venom sights - nice and low - need to use new 6mm screws)

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Re: Slow twist 9mm barrels

Post by robert84010 on 7/14/2016, 9:40 pm

Mac,
did you get around to fitting and testing your KKM barrel? There is another thread discussing the KKM in a S.A. XDM and it seems to work pretty well there also.

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slow twist 9mm

Post by Mac2 on 7/19/2016, 9:22 am

Dear Robert:   I did have the slow twist barrel fitted into 9mm Range Officer and fired it in a Bullseye match.  Inconclusive results.  No function issues.  Have attended Glock and Sig P320 armorer's school while trying to keep up.  Now I have a Doppler Radar velocity measuring device and will be able to collect more meaningful data.  Target set at 50 yards and will be testing using HAP 115 bullets and WSF powder.

side observation:  insides of P320 have many springs and it is very complex.  Significant manual dexterity is required.  Inside of Glock is much more simple.  As some wit wrote:  As smart and educated as FBI agents are, a couple hours training and they will be able to perform their own armorer tasks.  Do not try that with P320.

More details and numbers when I am able to provide.   Mac

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