@For those who are interested to convert Hatsan into a Gas Ram unit.See my design in the attached diagram. Hope you find it useful. Simple but very effective. You don't need to cut any part of the trigger housing as suggested by many Brazilian Hatsan tuners.
Yes, my gas ram has a 130 mm stroke. Hatsan needs a min of 120mm stroke.
As I have stated, Hatsan needs a min of 120mm of stroke. There is a preload of 5mm which is required for most if not all gas rams. Just look at my chronied numbers mentioned in my earlier threads. Now, after bedding the unit down with 2k shots, it is still shooting at 890 fps with 14.4 gr CPH and is still punching through 3/4" multilayered hardboard at 20 yds. I am very happy with the result.
My Hatsan is comparable to a new Hatsan 155 with an OEM spring that degrades overtime. When I decided to convert it, I was looking at a muzzle velocity of about 830 - 850 fps but was very amazed it surpassed my expectation. The recoil is sharp but NOT harsh, unlike the OEM Hatsan. The next thing I need to do is to replace the piston seal or convert the parachute seal to an O-ring ... will be my next project.