Rigging help

I am trying to rig this Flak 88, but I can not get the joints to work just right. The green circle is where I want the 88’s mount to turn, the red is where it currently moves. I know I did something wrong here; any help, please?

You have to place the bones in correct positions. My suggestion is you put it like this and link the bone that will move the barrel up and down to it. The tricky part will be making the barrel move in at shot (recoil), as linked bones can only be rotated, not moved. I dont have enough experience to help from this point.