Went to the range today with my 9mm Shield. The gun has only had approx 300 rounds through it. I cleaned / oiled it prior to going to the range. So, Not every magazine, but today 3 times during my 200 round range time the first cartridge required 2 trigger pulls. (yes, there was a round in the chamber and the mechanism charged to fire) The first pull is a trigger that isn't set- it just pulls all the way back with NO click. Pull the trigger again and that 1st round and all others in the magazine fire correctly.

Problem 2: 5 or 6 times today on the Last cartridge the slide failed to lock back- the slide simply returned to the full forward position.

Today was the first time these problems occurred. I've owned the gun for a couple of months.

Thanks!

I would clean and oil (lightly) the striker channel. It's a pain but there might be debris in there restricting the firing pin.

Problem 1. Could it be that your slide was very slightly out of battery, enough so that you didn't notice? If you slingshot the slide vigorously (don't "ride" it with your hand) when you chamber a round, an out-of-battery condition is unlikely to occur.

Problem 2. The slide is locked back after the last round when the empty magazine follower pushes up on a small tab connected to the slide stop. This forces the slide stop upward and allows it to stop and lock the slide in its rearmost position. If your follower is binding in the magazine, it won't fully return to its highest position and therefore won't push up the slide stop far enough to lock back the slide. Disassemble and clean the magazines, and while you're at it, check the springs for any irregularities. After reassembling, push the followers down several times, and make sure they return smartly to their highest possible position. Also, number your magazines so you can tell if the problem is associated with any one (or more) of them.

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What, me worry?

I had this problem early on with mine, even when slingshotting (worse if you didn't). Lubrication helped, but being sure the breech face was sparkling clean was also important, as the barrel has to ride up in that last 1/16" against the upper corners of the breech face.

Good point. As a part of each cleaning, I take a small brass scraper and remove the gunpowder residue from the perimeters of both the breech and the breech face. A surprising amount the stuff can accumulate there. I finish with a patch dampened with gun cleaner. I use only a lightly dampened patch on the breech face to avoid getting any cleaner in the firing pin port.

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What, me worry?

Thanks for reminding me of one of the reasons why I carry a revolver.

Sorry you're having some trouble...mine has been perfect. All four of my M&P's have been good.

Let us know when you get it figured out.

I had the same issue this week with my 100% reliable 45C. I quickly determined it was, in my case, that I loaded up a new load of 200gr coated lead bullets that were not letting the slide go fully into battery. I use the sling shot method of loading, and they just were no smoothly entering the chamber. I'm not sure what the fix is with these bullets, but that was my problem. You must go fully into battery for that trigger to set properly. If your gun is new it will straighten out by itself. It is probably just a tight fit.

As far as not locking back it could be a magazine issue, a slide lock issue, or even an extractor issue. Try each magazine to see if you can qualify a bad mag. If that doesn't work call CS.

I had a related if not identical problem years ago in 9mm. I'd been shooting my 9mm reloads (using Montana Gold jacketed bullets) through Glocks, Browning Hi Powers and a P-38 for years, but when my son got a SIG (I think it was a 226) his slide wouldn't always go into battery. Turned out that the lede in the SIG barrel was shorter than in any of my other guns, so the ogive on my bullets would engage the rifling in the SIG barrel just before slide battery, and keep the gun from firing.

The solution turned out to be seating the bullets just slightly deeper - I think it was about 0.015 that did it - and then all ammo worked in all guns. The powder charge wasn't near maximums so there was no real pressure risk from the additional setback, and I couldn't see any difference in functional reliability or accuracy from the "shorter" rounds.

Side not locking back may be something as simple as your grip pushing down on the slide release. Make sure you are not touching it with your strong thumb or support hand.