Check your extractor tension. If it's too high like mine was it can prevent the breach face from fully mating with the barrel causing light strikes. The extractor is 'opened' by the little ramp to the right of the chamber. If the extractor tension is too high the recoil spring has trouble pushing the slide back into battery.
You can check for that by slowly lowering the slide (empty gun of course) and seeing if the slide always goes into full lock up or if it stays slightly out of battery.
When I got my Kadet kit I had a lot of FTFs, maybe 15%, and ammo type didn't seem to matter. The extractor was very stiff. Took it out, polished everything, no help, the extractor was still very hard to move. It appears the hole for my extractor spring was not drilled deep enough, so I tried cutting a few coils off of the extractor spring. - Bingo! Now my Kadet runs like a top with any ammo. I use the stock 75B main spring.
Well, I did notice that my extractor was a little tight and the slide was not mating smoothly as you described. However, I had an interesting experience performing the mods. It took a while to remove the staked pin, and a lot more pounding than I wanted, but it eventually budged. Took out the extractor and spring, and decided to try trimming off one coil. No problems yet. But putting it back together, I ruined my pin in the process causing FTE and FTfeeds. So, here are a few things to learn about this process that I should have researched before hand.
1. When removing the extractor pin, push it out with a 1/16" (1.5mm) punch. Drive it out from the top of the slide downward (sit the slide down on a piece of wood top side up). There is a groove on the bottom of the slide for the pin to be driven into as you remove it, so you don't need to have a hole in the wood. Use gradually increasing force with your hammer until it budges, and then slowly tap it through.
2. Be careful removing the extractor/spring afterward. Put your thumb over the extractor as you remove the punch that you just used to drive out the pin. That way the extractor/spring won't just fly out into the abyss that is your workshop floor.
3. Thoroughly clean the parts, and the groove where the extractor normally is. There was some of the famous CZ packing grease in there on mine. I used a cotton cleaning patch and my punch to get in there to clean it out. It was pretty dirty, but probably not enough to cause malfunctions.
4. Cut your spring as needed. Then insert the spring into the hole with your cut end facing into the slide. You want the flat spring end to contact the extractor and not your fresh cut end. Push the extractor in the groove and hold it with your thumb while you insert your punch into the extractor pin hole as a slave pin to hold everything in place.
5. Pull your punch back a little so you can get your extractor pin started in the hole on the BOTTOM of the slide. Some needle nose pliers can help, but be careful not to mar the pin too badly with the teeth of the pliers. A little marring near the end may be good to re-stake the pin, but if you mar it in the middle near where the extractor rotates on the pin it will cause issues. Be careful here!!!! Slowly PUSH (do not hammer it) the pin in from the BOTTOM of the slide until it passes through the hole in the extractor and starts to go through the top half of the pin hole. You will have to use your thumb to hold the extractor down far enough to get the pin to go through. Once the pin is inserted as far as you can PUSH it, tap it through the remainder of the way with a slightly larger punch. GO SLOWLY WITH THE HAMMER, JUST TAP IT IN UNTIL FLUSH. Too much hammer impact will peen (mushroom) or bend your pin.
6. The pin was staked from the factory, so if you have a staking tool use it. Alternatively, you can use blue lock tight to "stake" the pin, but mine does not seem to need it. The pin locked in pretty well for me, but YMMV.
Things NOT TO DO!!!!
DO NOT - Insert the pin from the top of the slide with a hammer. I think the pin hole is tapered, and the hole on the top of the slide is smaller than the hole on the bottom of the slide. The pin itself is not tapered, so there is only one correct direction to insert it (from the bottom of the slide). It may look easier to insert the pin from the top down, but DO NOT DO IT! You have been warned. This is how I ruined my pin, and I was lucky not to damage the slide in the process.
RESULTS:
When I ruined my extractor pin, the result was terrible. I should not have even tried to test it, but I did and it was terrible with about 50% failures of various forms. After I replaced the pin ($2 + shipping is a nice cheap mistake, thankfully) the results are so far equivalent to before. I still see about 5% light strikes. I have only tested about 200 rounds, so I will update if things change.
I will continue searching. Thanks all for the advice so far
