How can bone names be copied across an axis? If an armature has been created with X-Axis Mirror enabled and we are renaming our bones to something more intuitive, and one half is done (example: arm_upper_L, arm_lower_L), how can we copy the names over to the other half of the armature?

I tried doing W Flip Names, but it did not take the names from the other side. I tried this with both the source side selected and then with the destination side selected, but I didn't get the desired result (which would be arm_upper_R, arm_lower_R).

I have been copy/pasting and typing in the difference, but if there's a better way I would like to know about it. What is the correct way to mirror the bone names over to the other side of an armature? Thanks.
make Sure you are in Edit Mode!

Step One: Create just ONE side of the armature and name the bones.

Step Two: Select Bones Wanted to copy to across an axis.

Step Three: Set 3D Cursor to origin by hitting Shift-S: 'Cursor to Selected' (Make sure origin is in center of armature).
Step Four: Press Shift+D and click the mouse button

Step Five: Hit Cntrl+M and then hit X (Or y if you are using the y-axis)

Step Six: Click the mouse button and hit w and select 'Flip Names'

Profit!