M&P 9mm FS accuracy "Looking at Clues"

[RStephen]

M&P 9mm FS. Stock as a Clock!
Mix of factory amo (Winchester) and reloads (within spec)!
Mix of 115, 124 and 147 grain bullets.
Factory dimple 1/10 twist barrel.
Production Date 06-2013.

Original groups at 25yd was 8-10"
Sent back to S&W. Returned with new barrel now getting 6-8" @ 25yd.

FYI... I asked S&W what "meets factory specs" and Range tested means and I was told that the range test is for function only, not accuracy.

Aftyer I got my M&P back and found that the new barrel only improved the accuracy slightly, I started looking at the brass.

Upon inspecting my fired brass, I began to notice that the primers on 70% have dimples from firing pin and then what look like a drag mark leading away from initial indentation. This to me looks like the barrel started to drop within milliseconds of ignition causing the wipe mark. If this is happening so quickly. I suspect the bullet has not had a chance to clear the end of barrel. Anyone else seeing this?

 

[DocSunShine]

How are you testing for accuracy?

 

[RStephen]

Bench rest, sand bags at 25 yards. Two different shooters. Can get 2" groups under same circumstances with g-19, kimber 45 and same shooters. One shooter is 4 times state champion and shoots competition several times a month.

 

[1sailor]

Try installing a heavier recoil spring. I installed a 19lb spring in mine and have no trouble with functioning. I did not have the same issues as you but it couldn't hurt to try and it's cheap enough. I would think that it may allow it to stay locked up slightly longer.

 

[JFR]

Try installing a heavier recoil spring. I installed a 19lb spring in mine and have no trouble with functioning. I did not have the same issues as you but it couldn't hurt to try and it's cheap enough. I would think that it may allow it to stay locked up slightly longer.

Agree with 1sailor...

The markings on the brass are common with M&P's but a stronger Guide Rod Spring will let you know if it's due to or is unlocking early as mentioned. For reference your factory spring should be about 16lbs. Note that it's easier to swap and test if you buy the whole guide rod assembly for just a few bucks more instead of just the spring.

 

[mjdupuis]

I just got mine back from S&W, for the same poor groupings. My production date is July 2012 and the barrel has no dimples. All they did were "barrel modifications." All I can see is a new, hideous crowning. They didn't buff it or polish it, just ugly tooling on a new, more deeply-angled crown. I was pretty disappointed that this was their solution, but until I shoot it I'll reserve judgment.

 

[serpentine]

Do you have pics of the newly tooled crown?

 

[mjdupuis]

Do you have pics of the newly tooled crown?

I don't, but can post in an hour or so.

 

[serpentine]

Thanks, that would be awesome. To the OP, I get the same little dimple on my Shield 9mm. I thought it was just normal.

 

[forrestinmathews]

I am very interested in this. I haven't gotten to stretch mine out to 25 yet. The majority of shooting for me has been at 7 yds with 147 gr and 135 gr older defensive ammo. Please keep us posted how the groups work out and what you did.

 

[mjdupuis]

To the OP, I've heard plenty about the odd primer marks and it seems to be common across the M&P platform. My Shield seems to leave more dramatic marks than my FS, though it shoots more accurately than the FS.
Not to highjack the post, but here are a few pics of the "barrel modifications," without a macro lens that's as good as I can get. The melonite finish is clearly gone and with the naked eye I can see the machining marks for the new crown.
It may do the trick, and for all I know (without having shot it, just got in yesterday) that's all that was wrong with it. But I don't think it is. There have been two new barrels released since this gun was manufactured. Why not just put the new barrel in?
I'm pretty certain my crown was just fine when I sent it off.

 

[Bkreutz]

To the OP, I've heard plenty about the odd primer marks and it seems to be common across the M&P platform. My Shield seems to leave more dramatic marks than my FS, though it shoots more accurately than the FS.
Not to highjack the post, but here are a few pics of the "barrel modifications," without a macro lens that's as good as I can get. The melonite finish is clearly gone and with the naked eye I can see the machining marks for the new crown.
It may do the trick, and for all I know (without having shot it, just got in yesterday) that's all that was wrong with it. But I don't think it is. There have been two new barrels released since this gun was manufactured. Why not just put the new barrel in?
I'm pretty certain my crown was just fine when I sent it off.

That looks like they used a drill bit and a hand drill. The least they could have done it hit the shiny parts with cold blue(or a Sharpie). I would have been ashamed to give that back to a customer in my gunsmith days.

 

[RStephen]

M&P arrived back at S&W repair today. Called and talked to supervisor. Supervisor said the markings are normal/typical of an M&P and are not an indication of accuracy issues. Discussed the accuracy I was getting and he assured me that what I was seeing would be fixed!

 

[scooter123]

Those firing pin swipe marks are typical with many semi auto's. My Sigs do the exact same thing and back when I could still focus on handgun sights I managed to put 10 rounds into a 1.4 inch group at 50 feet with my P229.

There have been a steady stream of sporadic reports about issues with the M&P 9mm unlocking early. So, that is a distinct potential cause for your poor accuracy. From an Engineering standpoint I can only see two potential solutions for this.

One is a stronger recoil spring as has been previously suggested. However, going from 16 to 19 lbs. is a rather large change and I would suggest that you may want to consider purchasing 3 springs at 1 lbs. intervals. Because if you combine a stronger than needed recoil spring with lighter powered range ammo you may find you have feed or ejection issues. Having a selection of springs on hand will make it easier to do a bit of fine tuning.

The second solution would require the services of a Machine Shop and re-finisher. So, it's really something that the factory should be doing. In this case the potential solution is to add a bit of mass to the slide to act to delay it's unlocking.

 

[RStephen]

Haven't posted in a while... Love the KKM barrel. Also had to put in the apex trigger kit. groups now down to 1.5" @ 15 yards.