I sent my 4.6" 10MM pistol back to S&W as it was having failure to feed issues. My note in the box read: "Evaluate / Repair, Polish Barrel/Chamber, Passed Range Testing".
I was inititally hopful that this would fix it, but I took it to the range after and the same issues persisted. I've tried heavier recoil springs on my own, but no luck the same problems continue. I think it may have something to do with the feed geometry from how the rounds feed from the magazine. It almost looks as if the cartridges are pointed too far vertically, the high slide velocity of the 10MM causes the failure to feeds.
I sent another note to S&W and I'll see if I hear anything back.