So, I polished all Trigger/sear contact points in my m400.

I have to say, it really helped the trigger. There was some gritty feel fight before the break. It's completely smooth now. It feels lighter also, but that is probably just the smoothness.

I used only polish and cloth, no stones so it took a while. I used a small screwdriver wrapped in cloth doused with polish on the hook of the hammer. I suppose a dremel with polishing attachment would have been better but I didn't have one. The trigger flats were easy so I spent some Tim on them.

Overall it was worth it. FYI