Don't use shims. Always use the same o-ring, that's what you're tuning. Follow the instructions in this post here to tune.
You should check
I've been in the same boat for years (ever since my school was the 4th or 5th school to get it) and then my dog made a Houdini escape and I couldn't find
No, I changed it to the drivers side, the passenger side was a mistake. With an off-set rail you can't get at the buttons because your tank get in the