My 23mm was something I tried a few years back now I fabricated the piston from some galvanised pipe, it started of at 79mm stroke with a titan no 9, heavy to cock but blisteringly fast , I now have it at 85mm stroke 180 grams , and a mark 3 spring, it cocks nicely, and is a much softer cycle , need to see if its up to snuff as an FT weapon, oh and its an o ring of course, Having tried two 22mm skirtless tunes I believe the full skirt with minimal rear bearing has less friction due to the better support , and they shoot much nicer in my opinion.