Ironwolf,
I have not had any feed or ejecting issues using lighter ammo. The lighter bullet weight seems to be offset by a greater powder charge in commercial loads. They usually have greater muzzle energy so there's plenty of impulse to operate the action. The Cor-Bon is downright hot. The main problem I have had with my P-40s has been that rounds, regardless of weight and worse with really open hollowpoints, like to nosedive into the feed ramp when loading by hand from a full magazine. When firing, this hasn't been a problem. So, I put one round in the magazine and chamber it. I then fill the magazine and insert it. As far as ejecting is concerned, it's reliable, but I usually catch a few cases on top of my head during a shooting session. There's little pattern to where they throw the empties.
One thing to be aware of is bullet setback. Not knowing your firearm knowledge, this is where the bullet gets driven into the case, reducing the volume and sometimes compressing the powder. This can cause dangerous pressures. .40 S&W is not very forgiving in this regard. I have some 165 grain Speer Gold Dot that seems prone to this. Some of these that nosedived into the feed ramp ended up shorter than fresh rounds. Banging around in the magazine due to recoil when you fire the gun can also cause this. Try shooting all but the last two rounds, that is, leave one in the chamber, and one left in the magazine. Measure them with calipers and compare them to undisturbed rounds. Hopefully they will be the same length. That Speer Gold Dot I mentioned was bought in bulk and was marked "Not for LE use. Practice ammo." I was told that this was because they were overruns and excise tax had been paid on them. Ammo bought on government contract has specifications for such things as how much force it takes to mash a bullet into the case. Perhaps these were really rejects for that reason. Being a reloader, I am now capable of putting a little more crimp on them and fixing them.
Other advice would be to replace the recoil springs regularly. Small powerful guns are hard on their springs. I don't see them on KelTec's Web site anymore. If they don't have them, Wolff Gunsprings has them and in various weights. I have used their 19 pound version with success. According to Wolff, stock is 17.5 pounds.
Your gun looks like it has a low round count. That happens a lot with these, and it seems like experienced shooters have more issues with them. If you are used to a full size service pistol, or heaven forbid, a really nice 1911, this gun is going to be hard to shoot. I found my first one while looking for a P-11. Since I didn't even know they existed, and it was my first gun in a serious caliber, I searched online to see what kind of trouble I was getting myself into and discovered this forum. I decided it was worthwhile to get to know this gun. I now have three, and strangely, shoot them better than I do my P-11. Go figure...
buzzsaw