anyone know what it is? or where i can find it?

My first armorer manual lists it at 1:18.75"; 5 groove right hand

I don't know if there's been a change since '07, though. The '08 revised manual didn't contain that info. You could call back and ask someone in customer service to look it up.

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Ret LE Firearms inst & armorer

thank you sir! so with such a slow rate the lighter bullets would probably be more accurate?

Dunno.

The 180gr load in .40 S&W still seems to be the dominant bullet weight when it comes to LE duty & training ammunition, and it was the original bullet weight around which the cartridge was developed, so you'd think they'd be optimizing their barrels for the more popular bullet weight(s), right?

But nothing surprises me anymore, though.

The M&P9 is listed with the same twist rate in that manual. (Hey, Glock lists the same twist/rate for 9/.40 in their guns, except it's 9.84" - different barrel design)

I thought I used to see twist rates in the 16" range for somebody's .40's, but I don't memorize such things and can't remember where I might have it listed (I haven't been an avid handloader for more than 20 years, and don't really have a need to have that info on the tip of my tongue as an armorer).

I just grabbed the last couple of M&P armorer manuals I had nearby to try and find it for you. (FWIW, it's not been exactly rare to find typo's in an armorer manual, so if it was something I really needed to know, I'd call and confirm with the factory, myself. )

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Ret LE Firearms inst & armorer

If you're a good enough shot to notice the difference in twist rates with a service auto, then I take my hat off to you.

(On reading my own post I realize that might sound snotty. That is not my intention.)

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Stu

Well, I, for one, didn't take it to be snooty at all. I immediately nodded my head in silent agreement, realizing you probably wouldn't have to take off your hat to me.

Now, when it comes to trying to stabilize different bullet weights in a .223/5.56 at 3200fps ... well, then it can become interesting.

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Ret LE Firearms inst & armorer

so the slow twist rate on these relatively slow moving pistol bullets doesnt have much effect?

Well, since S&W worked with Winchester to create the .40 S&W, I'd think they've pretty much figured out what will work best for their barrels, made by their methods, used in their guns.

I don't know what the Performance Center did in their limited runs of their specialty 3rd gen .40's, like the 5" model, though.

Why the query about the twist rate, anyway, if you don't mind my asking?

I don't think about much because I tend to stick to ammunition made by the major makers who have a lot of experience in making ammunition for LE/Gov users, and they have to produce loads to stay within specifications for various bids and contracts. If I can take my time and shoot rounds through just about the same hole at 10 yards, shooting unsupported, standing, 2-handed ... using a duty weapon (like a 4013TSW), loaded with whatever flavor of duty loads are being ordered at the moment ... I'm pretty much satisfied when it comes to a dedicated defensive/service weapon.

Why not call the Performance Center and ask to talk to one of their gunsmiths, and ask what they might be able to do to wring some further potential accuracy out of your particular gun?

Also, the TSW versions had larger box-type frame and slide rails, and larger front dustcover rails, which reportedly helped in achieving some better inherent accuracy (and the slightly delayed unlocking probably didn't hurt, either, since it was designed to help reduce the felt recoil impulse a bit). Why not look around for one of the TSW's?

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Ret LE Firearms inst & armorer

im just trying to LEARN about handguns and ballistics. i know in rifles slow twist= light bullets,fast twist= heavy bullets and in my target rifle it makes a huge difference in accuracy. i didnt know if the same principles apply as much to pistols or not and am trying to learn about them.

Cool.

Probably not so much. At least unless you're getting into some serious competitive shooting where custom barrels are permitted and such subtle nuances have been studied and analyzed.

In the years since I've been attending armorer classes for a handful of the various manufacturers of pistols commonly used in LE work, I've never heard an armorer instructor, engineer, repair tech or even a sales rep offer any specific warnings about duty ammunition made by the major ammo companies regarding bullet weight in their barrels.

On the other hand, in the 4 AR armorer classes I've attended, the importance of considering bullet weight & twist rate was mentioned in each of the AR classes. Seemed more important to the folks teaching the rifle classes (and at least a couple of the instructors were also teaching pistol classes at the same time).

Sure, there's always been the usual recommendations to use modern pistol ammo made to common industry standards, and that if one brand/bullet weight/load didn't perform well, to try another brand/bullet weight/load to see if it did better, but that was usually in response to questions arising from feeding, functioning & cycling issues.

You listen long enough and you can hear all sorts of things, though. I've heard a rep (not S&W) in an armorer class suggest trying a heavier bullet weight to try and resolve some functioning issues in one model of .40 pistol, and then heard the instructor recommend another armorer try a lighter bullet weight for a similar problem, also in a .40 duty weapon. (I idly wondered if maybe the two armorers might simply switch ammo between themselves to see if it helped. )

Anyway, I've been told that S&W spends quite a bit of money continually buying ammunition made by major ammo companies, for the purposes of testing, trying to obtain ammo representative of what is commonly used by their LE customers from time to time.

The M&P project was something like 4 years in the making, and since it was envisioned to become their major (flagship) LE/Gov product line for the company's future ... and S&W was pretty knowledgeable about the .40 S&W cartridge ... you'd think they would have probably done their homework and remembered their lessons.

I just don't know (never asked) if they intended their barrels to run better with heavier bullets for .40 caliber, or lighter bullets. Dunno if it matters or not, either. Sorry.

Clearly, I'm not anybody's idea of anything approaching an "expert" in this subject.

Still, it might be interesting to know what the PC does (if anything) when it comes to the twist rate of their competition 3rd gen .40's.

Anybody browsing this thread have one of the 5" 4006's, or know anything about the twist rate in the PC barrels?

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Ret LE Firearms inst & armorer

To piggyback on Fastbolt's comments: in the PPC game, open class revolvers (or whatever the heavy custom barrel ribsighted guns were called) typically used a 1-10 rifling twist for optimal accuracy with 148 gr wadcutter bullets at near air gun velocities in .38 Spl caliber.

Typical factory twist rates were 1-14 (Colt) and 1- 18.75 (S&W). If there was a noticable difference using service type ammunition, most folks weren't aware of it.

Frankly, given the limited range pistols are typically used at, I greatly doubt there's any practical difference in accuracy especially considering the limited weight range of most pistol bullets. Length of the slug is another thing entirely (as is significantly lower velocity) and is (probably) why the faster twist is successful in producing a useful increase in accuracy at 50 yards in that limited application (PPC).

It would be interesting to see if S&W made rifling twist changes in any of their purpose built target guns like the 952. I really kinda doubt it. I really lust after one of those, but I'll never pay that kind of money for one.

It's just a footnote to the conversation at this point, but I took the four-inch barrel out of my 4006 and looked through it. The land that hits the muzzle at 6:00 o'clock starts at the breech end a little below 3:00 o'clock, or less than a quarter turn. By crude observation you would get a little less than one full turn in 16"; so it sounds like a twist in the vicinity of 1/18 is approximately correct.

It always interests me to reflect on the actual spin speed of a projectile at muzzle velocities. If you have a bullet that leaves the barrel at 1000 fps with a 1/12 twist, it's turning once per foot, or, at that instant, a rate of 1000 times a second. Express that in RPM, and at that instant the bullet is turning at 60,000 RPM, or nearly three times faster than a high-speed router.

It's a silly thought experiment, except that it explains how you can shoot bullets into the surface of lake ice and find them stopped and spinning like high speed tiny gyroscopes.

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David Wilson

I hit the reference books about rifling twist in Colts. It seems Colt used a 1-16" twist in every centerfire caliber for standard pistols.

Sometime in the process, they changed the twist to 1-14" in the Officers Model Match revolver and carried this over to the Python also. 1-14 was also very popular in the heavy barrel conversions.

After reading "Twist and Shout" in the FEB/MAR 2013 HANDGUNS, and the FBI's standards, I am also interested in rate and twist. This apparently is becoming more of an issue for some reason. Very interesting article to this retired LE.

Jim Sr.

All I know of twist rate is the physics end of it. It takes more push to spin a bullet faster, and a faster traveling bullet can spin apart at high speeds.

I have a friend that had to custom order a new barrel for a target 6mm rifle because his bullets would break apart at super high velocities. He order a lower twist rate.

I'm sure the rate of spin required to stabilize a bullet is a pretty broad range, and for handguns we aren't that dependent on stabilization. Not like a rifle shooting 1000 yards or anything.

Also, handgun ammo moving at 1000 fps or between 800 and 1500 fps is relatively slow compared to 4,000 fps and up.

I would expect a .45 to have a faster twist rate than a .357 because the .45 is moving at half the speed. If it does not, that just shows the latitude we have in twist rates.

This is intriguing, and I may look into it. There has to be an optimum spin rate for a given mass or cut-section of a bullet.