I followed the same approach as RYO & P.A.Myers but different.

My issue was feeding reliable, sometimes every other would feed. And also had to shuck it real hard.

As the other guys the issue was in the Shell catch 330. Mine seemed to be hanging up or really hard activating the Shell release. It wasn't so much as the catch was holding the Shell after release lowered, it just wasn't lowering. If it was the catch not moving enough while release lowered you wouldn't be able to manually remove shells by pushing down release.

I filled parts 334, 331 and cleaning up/ light file on 330, 338.

228 will slide on 331 to release shells. Also will push on 334 into 330 pushing catch up to hold back the following Shell.
331 ,330 pivot on pin while 334 sides along and has recess to hold until slide is push forward to reset it.
When 334 is pushing into 330 it's also sliding against the part inside receiver housing 3008 this section is where 333 selector screws in.

Friction spots need to be filled down. I used small hand files getting rid of machining marks.

File holes for the pin in 331 & mainly 334. Careful with 334 not to completely file out recess. This step seems to make the most difference.
Second to this is the tip of 334 where it comes into contact with receiver housing section I was talking about & other side where it slides along 330.
Third but also important will be where 228 slides along 331.

Do at your own risk. I've only done light filing over all and helped tremendously.
I can rack as slow as I want with a slight pressure once I get to point where slide stop 228 meets 334 stop actuator. Also pressure when 228 goes forward to reset 334.

Video of feed in action.