Well the problem with the spring is that it will porpoise out of the hole sometimes as you lock back the follower to load the mag.
This is game endingly inconvenient...
What I did was increase the diameter of the spring only in one section, leaving a spring that looked like a python that just swallowed a rabbit. One section of larger diameter and the rest unchanged.
I identify what part to enlarge by cutting the hole, then slowly locking the follower back over and over. What I found is that the SAME section of spring was always the part to pop out, so I widened this section like this:
Just opening it and releasing it. With patience it's not too hard. I do a few rings then try it, if it still comes out i widen more of the spring. Essentially you're making the spring barely less diameter than the tube, this locks the spring into the tube for the section that matters. Most of it goes into the cup in follower or is held in by the end of the tube.
I hope that makes sense!
Once you find what size hole you want using the tubes, you can trace it onto the mag and then it's 'grind to the line'!