I purchased the SLP Mk1 this year to start shooting some 3 gun. The High Plains shotgun Challenge was the first event with the gun. I was running all 1300 fps stuff and thought I needed to be running the black ring or "heavy" piston. This only happened to me three times, but it would eject the old shell, and the new one would be started into the chamber sitting on the lift gate. I would just bump the bolt and it would go in. When I got home I email FN and the guy that responded basically told me to ignor the load weight published in the book and run the red ring "light piston" for all 2 3/4" and the black ring "heavy piston" for 3" only. I have since switched to the light piston and it ate 100 rounds of light clay loads without a hicup. My smith has moded the gate so it won't eat my finger, smoothed the loading port and made a custom bolt release assit. I love this gauge! Oh yeah...lightly oil the piston and keep the action wet.