Actually, now that I think of it, the '416 was running a ported cylinder and I used the stock full (unported) cylinder which came with the Pro-Win, even though I'm using a Systema MC51 6.04mm barrel (285mm) in a 10.5" upper.
Update : Pictures!
Sector gear damage
Piston teeth damage
Here is another interesting area of damage - the cylinder has been struck by something (I hope not the sector teeth) and deformed - Should it be replaced, and how can I avoid this. Do you think it might have been caused by incorrect disassembly, or not releasing the anti-reversal latch before separating the upper from the lower?
Thanks!