I have a Nikkor AF-S 600mm f/4E lens that I’ve owned for approximately two years. When on a sturdy tripod with a Wimberely gimbal head it articulates in all directions extremely smoothly, almost glass-like, with one frustrating exception. With the lens collar screw fully open and twisting the lens barrel within the collar, the lens barrel sticks causing a slight jerking motion with the initial twisting motion. Once moving, its motion is also extremely smooth. That slight sticking motion is enough to force me off target and bringing it back causes additional slight sticking that ends up causing me to fight with the lens. It is not a new problem and has existed from day one. I have regularly changed where I hold my left hand on the lens to minimize or help smooth the motion to no avail. Initially I thought since the lens was new it would smooth out over time, however that never happened. Yesterday I’m in Yellowstone shooting a cinnamon black bear and cubs during a comfortably cool, overcast, and humid day, and the “stick factor” kept pushing me off target each time I twisted the barrel trying to keep up primarily with the cubs in a tree. My question, have others experienced the same problem and, if so, what was done to correct the problem? I have thought about attempting to inject a dry lubricant into the fitting, but I can see no room to do that and I’m reluctant for fear of making the problem worse. Your thoughts would be appreciated.