Why do you have such tiny holes on the front of the cylinder?
Also the squarish notches in the back look like they're getting mushy when you smooth it. Can you show us a better close up of your geo, unsmoothed?
Looks good overall. Instead of trying to do lateral symmetry on it, it would have been better to use radial symmetry, model 1/6th of it, and then radial clone it around 5 more times. Not a big deal, but it's easier for future reference.
As for the index notches, just cut a couple of loops at the right position on the cylinder and then bevel them in. It's a square notch with a little divot taken out on one side. When you go to texture, keep in mind that the cylinder always rotates in the same direction, and there is usually a pretty strong wear line going around the center through all of those divots. This one doesn't show it because the finish is worn off all over:
Here's where these shots came from: