The cylinder insert works very well in my TX200 at 85mm of piston stroke, so some might be tempted to try it with rather shorter strokes, which I’d strongly advise against, for a variety of reasons.
First, a longer cylinder insert would eat into available spring room, and might necessitate using a stiffer spring, as would reducing the available piston stroke, which would sharpen the recoil, and might increase hold sensitivity.
Second, fitting my 11mm cylinder insert effectively increased the length of the transfer port from 9.8mm to 20.8mm, which caused a slight reduction in energy efficiency, although it was so slight that it was a price well worth paying. Fitting a longer plug, say 16mm, to reduce the stroke to 80mm, would increase the effective transfer port length to 25.8mm, which will cause a further reduction in energy efficiency; exactly how much of a reduction I can’t say without fitting a longer insert and testing, but what I can predict is that it would necessitate significantly higher peak cylinder pressure and temperature to maintain muzzle energy, and I don’t know whether the acetal would stand up to that.
In addition to the increased pressure and temperature necessitated by the longer transfer port, a potentially much larger increase could be needed to compensate for the reduction in swept volume, and consequent air mass available to accelerate the pellet. Taken together, the necessary increases in temperature to compensate for the increase in transfer port length and reduced air mass would take us into unchartered territory, just as I was 12 months ago when I fitted the 11mm cylinder insert. It might work fine for a while, but until it has powered 10,000 shots, it might not turn out to be reliable.