The full cylinder could have been a huge cause of your problems, because the compression is slowed at the beginning and doesn't reach terminal velocity till after the projectile leaves. If you're using a shorter barrel, I'd highly recommend getting a proper cylinder (Type 2).
Regarding the cylinder damage, I'm with Sha Do on his assessment... I'm also inclined to think that it was the sheared sector gear tooth dinging the cylinder.
My suggestion:
- Replace your cylinder with a type 2 cylinder
- Stick with your gear set
- If your piston tooth rack is mangled to the point of no more function, then replace it. No need to remove the last tooth on it, since the piston will already release once the last sector gear tooth passes. Although... you could still remove that last tooth if you wanted to save that 0.1 grams on weight so that the piston picks up speed that much faster... lol.
Tappet plate wear is possible from the high ROF. I'd keep several on hand if I were you. If you don't have any domestic sources for the tappet plate, give me a shout. I have two spare ones lying around here that aren't moving, so I can see if I can dump it to you at a good price. Hit me by PM if you want it.
Regarding the feed nozzle, I've never used the ProWin one before. I always replaced it with aftermarket ones, so I can't comment on that. If you are having feeding problems such as the BB not shooting, even though it's been loaded, this can also be a cause of your problems. If the BB is stuck behind the hop up rubber (the Pro-Win white hop up rubber is notorious for being too stiff and causing this), and if your air seal is quite good, a BB stuck behind the hop up rubber can actually cause the piston to return to battery very slowly and/or will not come to a complete rest, which will mean that for sure the sector gear will slam in to the tooth rack before the piston is ready to accept it.
Dynamo covered this issue as well.