I'm suprised at how much the velocity went up when the reg was turned down. A lazy closing valve doesn't always lead to higher velocity, but for sure more air used per shot...
I looked at mine breifly today, but think it is just enough different than yours as to not be of much help. As previously stated, mine doesn't have the Quatro, and I have no preload adjuster either...
Don't know how much work you want to put into it either. I think a much lighter striker spring can be used, as well as a lighter striker. As you may know, in my own valves I have gone to using a very, very soft return spring. Not much more than that found in a ball point, click type pen. I think that FX uses something along the same lines in many of their valves as well. It takes some doing to find just the right balance between striker weight, and pre-load, but when I hit it, it seems to work out well for a good shot string.
Anyway, have fun with it Walter. I look forward to reading your results!
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