Just to add to the discussion of different ammo through these:
Took my M3K out today to shoot it for the first time and test out the MOA Precision +6 kit I added. I decided to take the leftover federal shells I had kicking around. 35 or so of the red, white, and blue 1 1/8oz at 1145 fps, 25 of the 1oz at 1250 fps, and 25 of the 7/8oz shot at 1200 fps - all 8 shot. The 1 1/8 went first, I had a few hiccups in the first few rounds and figured it might still be tight out of the box, or, more likely, I wasn't leaning in enough with my short, stick-figure build. the remaining 1 1/8oz went just fine. There might have been one FTE mixed in that I forgot to put in my notes, but as best I can remember it did well past the first six or seven.
Then I went straight to the 7/8oz and got to use my new M3K as a single-shot for 24 straight rounds, all FTE. The final one (barely) plopped out the side.
The 1oz shot had one FTE, ironically on the very last one.
As I have read, semi-auto shotguns tend to not like slow, light loads, such as the 7/8 I was using. I don't know much about shotguns just yet so I figured 1200 fps could maybe help make up for the light shot. I was wrong.
After reading about these extraction issues with cheaper ammo, I'm going to buy more of the cheap federal stuff that did cycle today to see what the longer-term reliability looks like or if there is a type that does work better. I'll also be bringing the Winchester AAs out next time, which I'm hoping will cycle real nice.
All in all, the trigger is a but clunky but I didn't have much trouble popping clays with it so I'll leave it be and see what I think once I start getting better. The MOA precision/Nordic Components +6 kit worked great with the spring cut to the recommended 16" past the installed tube. I also put the MOA Precision follower in. I never fired it with the stock follower so I don't know if it was any better but it pushed shells every time so... there's that.