Make sure your choke tubes are tight before and while shooting! Loosen them up 1/4 turn or so when you're done.
Barrels expand ever so slightly with heat, and choke tubes can get stuck. It's best to keep them loose, but shoot with them tight to avoid damage to threads.
The long extension on the right of the picture is probably to pop out the pins that hold in the trigger group. It should come out as a unit, and make cleaning really easy.