So... Got the Apex extractor and installed it today. Took the M&P out to the range and tried it out... I gotta say... This part has cured my problem! I only ran 100 rounds through it, but had zero problems. And this was with full power, 200gr bullet at 1200 fps loads. I will keep monitoring it, but I have to say thanks to Apex for helping me get this thing reliable. I played with magazine springs, recoil springs and everything else, but before I installed the Apex extractor, I couldn't get through one magazine without failures to feed, failures to eject and loaded rounds puking out of the ejection port. Today's test was with the stock magazine springs, and the 24lb recoil spring.

This fix was suggested on a FB  M&P page.   The explanation I got I will paste below from Scott Folk at Apex:

Scott Folk:
  "Most people don't realize that the extractor in a pistol is integral to the feeding process. The stripper rail picks up the top edge of the brass to advance it forward out of the mag. As the bullet rides up the feed ramp, the rim of the cartridge slides up against the breech face, but not flat against, the bottom edge is away from the breech while the top is against the breech. The extractor has to be cammed out by the case rim against spring tension. There is a necessary feeding cut on the bottom of the extractor that helps cam the extractor out, we call it the feeding cut. What we found on the m&p extractors is that the feeding cut angle is not optimal and often creates too much tension against the case. In the case of a 10mm, due to the radius of the cartridge and speed of feeding, often the case jams against the entry cut causing a feeding malfunction, or the extractor can't cam out which causes the brass to pop off the breech face.
At Apex, we happened to receive 2 10mm that wouldn't feed for Jack. I did some experimenting and determined that the pistol would feed cleanly without an extractor, which meant that the extractor was the cause. We did some magic Apex Voodoo that we do and we're able to create optimized feeding geometry.
When the original m&p launched, mine had terrible extraction, it was so bad that in a uspsa match, my long rotating transition was fast enough that I caught a piece of brass on top of my slide between shots. This caused us to redesign the original m&p extractor and call it our Failure Resistant Extractor or FRE. We applied a similar technique to the Glock gen 3 extractors and were able to drastically improve the ejection pattern of the G3 platform.
All this is to say that we've been doing this a long time and we've gotten pretty good at fixing feeding and extraction issues at Apex."

So I found this today on YouTube about the possible issues I am having with this gun, and as most of you have said, it is related to weak magazine springs.  Worth the watch if you are having this problem.  I ordered a set of Springer Precision Magazine Springs today.  Will report. Greybreard, I did check out the barrel fit as per the information you supplied.  No problems there.  This pistol is not going to win.  It will function, just gotta get it sorted out.


https://www.youtube.com/watch?v=DXb8_MNLvPk   

So yesterday I took the new magazine out to the range.  It did seem to perform better, but still not 100%.  I also installed a +10 Wolff .45ACP spring in one of the other magazines.  Didn't seem to make much difference.  Still getting these stupid failure to feed malfunctions, but hey, at least this time it only puked one loaded round out of the gun!  I don't understand this, as it runs my standard .40 S&W load fine, with no problems.  Which is stupid, because if I wanted another .40, I would have bought one.  Attached are pictures of the malfunctions I encountered while running some book safe, but honest 200gr lead flat points at a chronographed average of 1200fps.  Still looks like the slide is outrunning the magazine spring. Still using the 24lb. Wolff recoil spring.

I have been having the same "loaded round ejection" problem with my 4.6" gun, as well as it seems to like feeding the odd round into the barrel hood instead of the chamber.  I installed a Wolff guide rod and 24 pound spring and it helped, but didn't completely resolve the problem.  I installed a Wolff extra power magazine spring in one of the mags and that cut down the failure rate a little bit also...  Today I was out at the LGS and they had 10mm magazines, so I snagged one.   Once I got home I took it and the other stock magazine apart to compare them.   This is what I found:

The old spring is at the top, the one out of the new magazine on the bottom.   Neither one of these magazines had been disassembled before.  See the problem on the older mag spring follower?  So now I'm wondering if anyone else has checked this on their malfunctioning guns and found that the follower was installed backwards at the factory and if that could be a cause of all of our feeding problems with these guns.  I haven't had a chance to run out to the range and test the theory myself yet.