Animation problem

I’m trying to animate a Gatling gun for a side project I am doing while messing around with Blender. Now the gun is pretty much built and the rotation of the barrels works well in object mode, but when I go to animate it there is a slight wobble that I can’t figure out how to fix. I tried different pivot points and re-sizing the feed point into the barrel, still nothing seems to get rid of this odd wobble. Any suggestions?

Is the gun barrel rotational axis in-line with global coordinate?