Circles, angles, and edge splits

If your Edge Split modifier is set to 30° (by default), then you should never add circular shapes with less than 13 sides to them. Why? Because a 360-degree circle divided by 13 sides equals approximately 27.7° per side.

Any fewer sides and your angles are going to break the 30° mark and become sharp. So, 13 is the mathematical minimum. In practice, however, it's not an easy number to work with.

You can't cut it into halves or thirds, and each angle is a long decimal number (27.6923076...). This makes it hard to rotate something (such as a cut out) around a cylinder by "one side".

Instead, I suggest using a minimum of 16 sides per circle. It's easily divisible by factors of 2, and the angles work out nicely.

Next, we'll add a Shrinkwrap modifier to our circle object, and press it up against the gun. This is exactly the same process that we just used cut out the large circle.

Just like before, apply the Shrinkwrap...