I got this cylinder to replace the cheap aluminum stock cylinder that came with my ASG AW.308 (Type 96). I was a little hesitant about the teflon coating, but for the price, I was willing to give it a shot. Over all, it is decently constructed, a solid feel, and a nice weight (I prefer heavy cylinders, rather than light ones that could warp easier). The teflon coating is a lot more durable than I expected, and actually provides a much smoother gliding action for any nylon piston washers than polished SS. The piston seal seems fine, and will likely provide enough of a seal for most standard upgraded springs, however if you plan on using a crazy spring, then a polished SS cylinder would likely provide a better seal. I did notice that the cylinder head had a sharp edge at the nozzle opening (where the BB sits), but a little light sanding with 150 grit paper or deburring tool easily removed that. The only big flaw, for my rifle, is that the machined nut on the end is smaller than the nut hole in my bolt arm assembly. the length is correct, but because it is smaller, the cylinder is not held at that point from rotating slightly. To compensate, I just had to tighten the cylinder screw really well (maybe some thread-lock?) and just keep checking that it hasn't loosened.
I don't expect the teflon coating to last forever, but I purchased this knowing that, and have added some nylon rings in my receiver and smoothed up any edges that come in contact with the cylinder.
Very true (straight)
Smooth action (with nylon guides for piston)
All around good value
Sharp lip on cylinder head (easily removed)
Incorrect sizing of machined nut fitting at the end of the cylinder (for ASG AW.308 rifle)
Teflon coating can wear off (no way around this, teflon coatings are what they are, a coating)