A Cause of S&W M&P9 Inaccuracy

[Jaywalker]

Introduction
I posted this yesterday (on page 26 of a different thread and in slightly different format) whose topics wandered as they tend to do. In order to see if this has any merit I'm posting it now separately. I'm proposing a model that explains some - but not all - of the well-know S&W accuracy problems in order to provide a conceptual framework for those (including me) who have struggled to understand the "why" of these problems. As we say in experimentation, even if it does not prove to be valid, we've at least provided negative data points... If it's valid, then we may have a way forward.

Issue
Smith & Wesson M&P9 pistols (9mm) are pleasant to shoot and have good ergonomics but suffer from accuracy problems that show up at 25 yards but are not always apparent at shorter ranges and are generally not also present in their .40 and .45 caliber models.

Hypothesis
This hypothesis holds that in order to keep recoil forces and slide velocity under control in their lighter-recoiling M&P9, more material is removed in production from the slide than from those of .40 or .45 caliber pistols. This lower thickness is then more subject to distortion when undergoing heat treatment than the thicker slides (this is the heart of this hypothesis). These resulting warped slides observed by others are then the cause of some of the reported inaccuracies. Warped slides explain why barrel replacement is not a fix for all of these pistols with accuracy problems - this has been observed by others. (If it is not true that M&P9 slides are thinner in places than those of .40 or .45 calibers, then this hypothesis fails.)

Possible Verification Test
The hypothesis should be easy enough to test. As I understand it (not having an M&P), you can fit a 9mm barrel in a .40 cal slide. If it performs poorly in the 9mm slide but properly in the 40 slide, then we're on our way to an answer, if not a solution ( a "solution" would be up to S&W). I do recall, however, that Bill Riehl discovered some suspect barrels (chamber concentricity, etc.), so I wouldn't expect those to work well in any case; a barrel may mis-perform in both slides.

Disclaimer
Data on warped slides and non-concentric barrels certainly came from Bill Riehl's testing. Other observations likely came form several combined sources. I'm neither an engineer, nor a gunsmith, so I'd be interested in hearing the no doubt infinite ways in which this is wrong... Please let me know what you think.

(Okay, the format's a bit overwrought, but I've been retired for awhile now, and who could foretell that I'd miss formal written reports?)

[Wayne Dobbs]

The warped slides caused by Meloniting was a big factor, that has reportedly been addressed by no longer doing this process.

I predict this will be an epic thread and I'm now waiting on Bill Riehl to sound off.

[orionz06]

To add to that does anyone know the details on if/when S&W switched who did their finishing? I had been told that some point along the way they switched the company who did the slides. My two best M&P's (2.5"@25 yards or less) were made before this supposed switch and once it was supposedly switched the issues became quite prominent.

[Sasage]

So the PVD finishing process on the 151215 would in theory remedy the issue?

[SecondsCount]

A couple thoughts from a guy who has an electronics engineering background so take it for what it is worth.

1. Why, if the accuracy issue can be attributed to slide warpage, do the 40 S&W versions shoot fine? Is there really more material removed or is this a theory?

2. Does the 9mm M&P really get less accurate at 25 yards? A 1" group at 5 yards will naturally be 5" at 25 yards so are shooters just not realizing that? I can see this being a viable theory if the bullet is not being stabilized by the barrel but am having a hard time thinking that it would show that much at 25 yards.

3. Why is it that the M&P9 seems to shoot really well with heavier bullets. 124 and 147 seem to shoot better than 115. Julie Golob even mentioned that her M&P has a factory barrel and shoots great with 147 grain loads.

4. People have replaced their barrels on the M&P9 with aftermarket barrels and have seen a big improvement in accuracy. I have a good friend who had G&R put a Storm Lake barrel in his M&P and wrote about it here.

The M&P9 that I had was a newer generation. It shot fine for me with 124 grain reloads. The guy who I traded it off to shot it with 115 grain Federal ammo and it would throw a flyer every 3-4 shots. His Gen3 G19 was shot the same day, with the same lot of ammo, and did not have this issue.

I have a factory 9mm barrel and a M&P40. The 9mm barrel is not a tight fit in the 40 for obvious reasons but I have put it in the gun and it ran fine. I have not tested it for accuracy.

[1slow]

Some have reported changing barrels to no improvement, there seem to be multiple factors involved.

[JHC]

I think the reason we see 1 inch groups at 7 yards is because of people. Good guns would probably do .355" groups at 7 yards. I concluded my 5-6" @ 25 yds (rested) M&P was jacked up because I could set it down and pick up the Gen 4 G17 I was 2K testing at the same time and shoot 2" (rested) with the same loads. But with either of them, shooting at 7 yards, they looked about the same. Other than something about trigger control and the shooter, 7 yds is not very informative to me.

[orionz06]

A paster sized group or smaller at 5 yards is what many strive for. 1" being almost twice that. 5" at 25 is still close to twice what other guns do.

[Wayne Dobbs]

I don't pay much attention to close quarter groups. Until I get a pistol at 15+ yards and test it, I know absolutely nothing. And 15 yards is where I found my first M&P 9 was a turd. I was doing some of my structured B-8 bullseye work with the gun and started noticing that impacts were not matching up with my shot "call" on the shots. Bench testing at 25 yards showed that I was the proud owner of a pistol that was capable of 10 shot groups of 8-10" with anything I tried in it.

[Jaywalker]

1. ...Is there really more material removed or is this a theory?

That's indeed the question. As I mentioned in the last line of the "Hypothesis" paragraph, if slide thickness among the calibers is the same, then the hypothesis fails.