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MH64
08-25-12, 00:57
So what do most pistol manufacturers use as the twist rate in 9mm handguns?

skyugo
08-25-12, 01:06
glock and HK use about 1 in 10.

LightningFast
08-25-12, 01:19
glock and HK use about 1 in 10.

Yep. CZ 75 and the like use it as well.

S&W M&P uses something like 1 in 18.5, IIRC.

skyugo
08-25-12, 02:58
Yep. CZ 75 and the like use it as well.

S&W M&P uses something like 1 in 18.5, IIRC.

hmm that's quite a bit slower. interesting

TiroFijo
08-25-12, 09:29
From a gyroscopic stability standpoint, 1-18.5" is plenty. S&W uses 1-18.75" for 38 spl and 357 mag, which use longer, heavier bullets across an extremely wide velocity range with excellent resutls. There are custom barrels that use even slower twists, looking for best accuracy. The 9 mm bullets are relatively short and very easy to stabilize, and the reason 1-10" is the standard is simply tradition, NOT reasoning.

If the S&W MP 9 mm pistols have some accuracy problems, it is likely due to other reasons, not twist. The vertical spread that some report is an indication of early unlocking.

LightningFast
08-25-12, 12:47
From a gyroscopic stability standpoint, 1-18.5" is plenty. S&W uses 1-18.75" for 38 spl and 357 mag, which use longer, heavier bullets across an extremely wide velocity range with excellent resutls. There are custom barrels that use even slower twists, looking for best accuracy. The 9 mm bullets are relatively short and very easy to stabilize, and the reason 1-10" is the standard is simply tradition, NOT reasoning.

If the S&W MP 9 mm pistols have some accuracy problems, it is likely due to other reasons, not twist. The vertical spread that some report is an indication of early unlocking.

From what I've researched and gathered, the contrary proves true. High speed video testing showed inconsistent unlocking, not consistently early.
Also, if stabilization is not the issue... why do almost all M&Ps shoot well with heavier grain bullets (147), but it is a crap-shoot with 115s?

skyugo
08-25-12, 14:09
From a gyroscopic stability standpoint, 1-18.5" is plenty. S&W uses 1-18.75" for 38 spl and 357 mag, which use longer, heavier bullets across an extremely wide velocity range with excellent resutls. There are custom barrels that use even slower twists, looking for best accuracy. The 9 mm bullets are relatively short and very easy to stabilize, and the reason 1-10" is the standard is simply tradition, NOT reasoning.

If the S&W MP 9 mm pistols have some accuracy problems, it is likely due to other reasons, not twist. The vertical spread that some report is an indication of early unlocking.

I kind of doubt that twist rate would have a lot of effect one way or the other at pistol velocities and ranges...

agreed, the m&ps with issues probably have something weird going on at lockup/unlock. Honestly every M&P 9 i've shot (3-4 of em) have been tack drivers though. I always go through a brief period of wanting to ditch my g19 and go full M&P after shooting one.

saddlerocker
08-25-12, 14:52
From what I've researched and gathered, the contrary proves true. High speed video testing showed inconsistent unlocking, not consistently early.
Also, if stabilization is not the issue... why do almost all M&Ps shoot well with heavier grain bullets (147), but it is a crap-shoot with 115s?

If a slow twist rate was an issue the opposite would be true.
115gr would be better than 147gr

TiroFijo
08-25-12, 16:44
From what I've researched and gathered, the contrary proves true. High speed video testing showed inconsistent unlocking, not consistently early.
Also, if stabilization is not the issue... why do almost all M&Ps shoot well with heavier grain bullets (147), but it is a crap-shoot with 115s?

when I read things like "almost all M&Ps" I wonder what is really the statistical certainty of this claim...

I haven't seen any high speed videos of these pistols, do you have a source or a link? I wonder how "inconsistent unlocking" would happen without the "early" part. I don't see it possible, the unlocking timing is basically fixed based on the momentum equilibrium of the accelerating bullet and powder mass and the mass of the slide+barrel, and the geometry of the unlocking mechanism.

spr1
08-25-12, 17:32
When questions of the M&P's 9mm twist rate come up, I always think that if S&W wanted to ensure that the twist rate was not a problem, that instead of doing any calculations and testing, that they should just copy HK and then spend their time worrying about things like unlocking.......

TiroFijo
08-25-12, 19:06
As stated before, there is plenty of evidence that twists of 1-20" and faster are excellent for accuracy on all availble bullet weights. Of course individual pistols may have a different bullet type and weight preference, for some unknown reasons... but the groups would be within "normal" limits. In any case, the very large groups that some have reported of M&P pistols are likely not due to twist but to faulty unlocking geometry.

The 9 mm 1911s usually have a twist of 1-16", mainly because US barrel makers try to standarize all calibers to this twist, that works very well for all normal handgun claibers.

The KKM replacement barrels for the M&P are 1-20" and reportedly are very accurate. Storm Lake are 1-16".

Edited to add: many custom competition 9 mm pistols use 1-24 or even 1-32 twists and are extremely accurate (1.5" at 50 yds), but the bullet velocity is usually high, and bullet weight only 115-124 gr. That's why a faster twist is better for general use.

LightningFast
08-29-12, 15:24
when I read things like "almost all M&Ps" I wonder what is really the statistical certainty of this claim...

I haven't seen any high speed videos of these pistols, do you have a source or a link? I wonder how "inconsistent unlocking" would happen without the "early" part. I don't see it possible, the unlocking timing is basically fixed based on the momentum equilibrium of the accelerating bullet and powder mass and the mass of the slide+barrel, and the geometry of the unlocking mechanism.

You seriously are unable to see that "almost all" prevents an ultimate claim? If you want to nitpick things that much, go ahead. I'm not going to engage in any further conversation with you.

For the high speed videos, I will try to find the exact one. Though I'm sure there are a number available. I will edit it into this post.