Here are the modifications I made to my RTI ARMS Prophet II.
New valve
Sharp edges of the barrel
Pellet pusher
Connection rod
O-ring on the other side of the valve
TPU lid
Here is the video from Amazing Airgun channel
FX Barrels. 4.5 minutes the part I mentioned about sticking
https://www.youtube.com/watch?v=64aFCZa2mUw&t=6s
Guide to accuracy
https://www.youtube.com/watch?v=Uj7xpjniMBU