M&P gen 1 9mm heavier recoil spring improve accuracy?

M

marine6680

New member
Here is my line of thinking...

There are several reasons floating around on why the first gen M&P FS pistols had accuracy issues. I believe it is due to the barrel unlocking too quickly.

At least on both of my FS M&Ps anyway... The barrel begins to tilt down with even the slightest slide movement.

I am thinking a heavier recoil spring could delay the movement of the slide a bit longer, and it may help reduce the effects of the barrel tilting so quickly.

The effect may be too minor to be worth it though.

Swapping the recoil spring in my VP9 to the new heavier version (same as the 40s&w version) H&K recommends, is what got me thinking on this.


I am thinking of getting an Apex semi drop in barrel for one of my FS M&Ps, as it is my range toy with a tuned trigger and all.

The other is used in a defensive role and will remain as is. If the concept of the heavier spring holds up, it may be worth a shot.
 
M&P gen 1 9mm heavier recoil spring improve accuracy?

My initial thoughts would be that the spring itself wouldn’t be enough. Apex made their improvements by changing the locking geometry on the barrel IIRC. Yes they’re two means to an end but I think the difference in those means isn’t negligible. My guess is the amount you’d have to increase the spring weight to achieve the same result will compromise function.


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Gun manufacturers work long and hard to figure out the proper spring weights for their guns.
Why does everyone think they know more than the designers?
 
My initial thoughts would be that the spring itself wouldn’t be enough. Apex made their improvements by changing the locking geometry on the barrel IIRC. Yes they’re two means to an end but I think the difference in those means isn’t negligible. My guess is the amount you’d have to increase the spring weight to achieve the same result will compromise function.
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Yes, the Apex barrel changes some things to prevent the early unlocking.

The VP9 now comes with the same spring as the VP40, it is a very noticeable increase in spring weight. I got one from H&K to put in my early VP9, and it ran fine, even with some middle range reloads.


Gun manufacturers work long and hard to figure out the proper spring weights for their guns.
Why does everyone think they know more than the designers?
Click to expand...

I am sure H&K worked long at hard too... But the change to a heavier spring still happened after a year or more of production.

The M&P does have an accuracy issue as ranges increase, so the engineers were not perfect.

I am just thinking of ways to improve the problem simply.
 
The VP9 now comes with the same spring as the VP40, it is a very noticeable increase in spring weight. I got one from H&K to put in my early VP9, and it ran fine, even with some middle range reloads.
Click to expand...

But again the question is how much stiffer do you need to have it to make a noticeable change? It may only be as much as say the newer spring in the VP9, or it may be more than that. I would say to me M&Ps seemed stiffer spring from the factory than the early VP9s to begin with, but I never measured them on a gauge.

In the end it's your pistol so really you can do whatever you want. If it doesn't work you just put the factory spring back in. Not really a big deal.
 
I don't think it will make a lot of difference, but springs are not very expensive.
If you buy Wolff round wire springs you will have to buy their guide rod.
ISMI flat wire springs will fit the factory rod but are not made in as many load ratings.

The Apex barrels have different lockup and their 10 twist rifling holds the barrel in place a microsecond longer by torque reaction, nothing to do with bullet stability. But they aren't cheap.
 
This is really mostly conjecture...

I would need to have access to some equipment to really know.

It could be that the spring rate is fairly heavy as it is, and going heavier would cause problems.

Spring rates can cause a delay in the slide cycling, but how much is the question, and can any required delay be obtained with a spring rate that allows proper function... That's the question.

As I said... Need equipment... A good high speed camera could tell the tale.


S&W also uses a 1 in 10 twist now, but that didn't fix all of the problem.
 
S&W also uses a 1 in 10 twist now, but that didn't fix all of the problem.
Click to expand...

Apparently had no effect. They couldn't tighten up the fit on a mass produced gun to where fine tweaks like that would help.

But he doesn't need a high speed camera.
A sack of springs and a target will tell the tale.
 
FWIW I own a first gen 9mm FS and the 40 FS and I have switched the springs and the gun runs fine. In the end I just put the factory spring back in since I haven't had any issues with my 9 FS but was just curious if it would run.

The 9mm FS has a very low spring rate. I'm not sure what it is but my 9 FS will pop out of battery with the slightest touch and the 40 is not like that at all.

At this point I would not spend money on a first gen gun at all. Get the 2.0 and be happy.
 
If I were in the market for a new FS 9 mm I would look at the 2.0. But I love my first Gen M&P 9, shoots great, holds nice groups, and is my EDC.
OP: try a new spring and see if that helps with your desired results. But you can chase "perfection" forever and still have a gun that shoots about the same as it did before.
 
They both shoot fine out to around ten yards or so... Then groups begin to open up significantly... More than simple deviation from distance would account for.

I have shot the 2.0, and it shoots much better from what I seen.
 
On the S&W Forum, one of the Apex employees (Randy Lee, who designed Apex barrels for version 1 and version 2 of the M&P) mentioned that there was a slight amount of slide stretch (which returns to normal after each shot) observed in the original slide for version 1. This was noted when Apex did a lot of high-speed digital imaging trying to figure out what was going on. You can see the entire discussion if you search on the topic: "M&P M2.0 Accuracy Issues, do to dwell time?" (I know they don't like links to other sites...)

S&W changed the M&P slide slightly with version 2, and the stretching was ONLY an issue with the 9mm version, which was thinner in the "problem area" (which was near the ejection port); other caliber M&Ps were more robust in that area.

That said, I've never really understood WHY it was an issue IF the amount of stretch was consistent from shot to shot -- as consistency in lockup is supposed to be one of the critical factors in accuracy. Given that the "stretch occurs BEFORE the bullet leaves the barrel, so there can be some variance in the slide/sight relationship, but it seems that the frame ought to stretch the same amount with each shot as long as the rounds fired are relatively similar in performance.

Maybe slight differences in round performance has a greater effect on accuracy if the slide can stretch? I've obviously got a lot more to learn about gun design...
 
Interesting read.

From what I understood... The barrel has very limited vertical support, just the pressure of the takedown lever against the barrel lug... But that support is weak, and temporary.

The stretching allows the barrel room to move, and due to the weak vertical support, it tends to move in the vertical direction.

The problem, is that the forces are never identical from shot to shot, so the amount of movement varies. This is the cause of the issue.


So a heavier spring may not do much... It may help keep a bit more pressure on the barrel though, so it may do something noticeable... Maybe not.
 
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