I suppose you're using the default unity mouse look script? In that case there should be a property like min and max x . In the same state you use to rotate the empty, drag in the script component from the inspector right into the playMaker action tab, and then release the mouse button there. That should give you the option to get or set a property on that script. Choose get property. Then drag it in again and choose set property (do this for both min and max).
Now, this is sounding a bit tricky, but it's simple, really.
Create 2 new float variables called MIN and MAX . Duplicate your set and your get property actions. Then set the one up, so you get the minimum X and save that to MIN. Set another up so you get the maximum X and save that to MAX.
Then do the same for the 2 set property actions. Make the set property actions every frame (just the set, not the get).
What we've got now is, it gets the min and max X values from the script and applies them every frame to the same script. So nothing should change really, other than that state probably running forever.
Now next is the fun part. Now that we have the min and max values we can actually change them however we like. The most convenient way would be the ease float action, which works like iTween move.
So let's say your gun recoil is 30 degrees and happens over 0.4 seconds linearly.
What we do is use "ease float" and tween the min and max values to a new pair of variables, let's call them NEWMIN and NEWMAX. So before the ease float actions, add a pair of float operator actions. They'll look something like MIN + 30 = NEWMIN . (same for NEWMAX).
So what should happen now is the gun should start to recoil, and as it rotates, the Minimum X and Maximum X on the script should update every frame to a new value which just as fast as the camera recoils turns from it's initial MIN and MAX values to the NEWMIN and NEWMAX values.
So without any noticable restriction if you look way up, the min and max values will always allow you to look around just like you did before.
I hope this made sense. My ideas are never simple I know