My Sport came with the 10rnd ASC. No issues whatsoever. I have grabbed a gag of Thermold 10rnd mags as junker target mags. They have also been flawless ($7..... bargain!)
My first impression is the chamber needs a decent cleaning and polishing. Bore cleaner foam, and then use a chamber cleaner brush, or really any brush that will fit it. Many rifles are shipped with a packing oil in them, it makes them sticky right out of the crate. It's really heavy, tacky stuff made to stay put for months on end in storage.
Then, open the rifle as for cleaning the bolt. Press the buffer tube back manually, and give it a small shot of lube. Pump it back a few times; a sticky buffer can screw stuff up.
Next on the list, the magazine. Check to see the feeder is not hanging up. (I doubt it will, ASC are good to go.) If sticky, depress and give a light shot of lube. manually load and then thumb dump the ammo, see if the rounds stick at any point.
Last issue; look to the feed ramps. Rifle open, and you will see where the bullets actually feed up into the chamber. There are 2 wider ramps at the bottom. That all should be pretty well lined up. If it is off, then you might have an issue and have to send it back, or get a smith to adjust it for you via S&W warranty service. (Easier and quicker than sending it back. Most companies will do something small of the sort if necessary.)
Another thought, load a mag, and sprits the top of the mag so the first rounds head in a little wet. Sometimes, it's a drop of lube missing and it causes issues.
With this all said, my Sport has been stupid-reliable. This is a small thing, 90% guarantee it's lube/ cleaning related.
