So I recently pulled out an old controller for the original xbox out of my closet. I was going to convert the end and give it to my cousin since we've started playing mugen weekly. I noticed that it had a circle gate on it and it felt WAY better than the "better" stick I was using.

Since I opened it up to redo the wiring I investigated the stick. It had a square gate on it, but it didnt actually make contact with anything. The stem made itself into a circle gate for all intents and purposes. I wanted to see what mine did. 6 screws later and I was on a mission.

I have the soul calibur 4 Hori stick
You can see the SC4 and original versions. If your stick looks like either one you have the same EX2 stick. I consider it a beater. It's tough, has some weight, and all in all was pretty reliable. The EX2 sticks come with a square gate. Unlike the $20 xbox1 controller the stick actually makes contact with the gate. I viewed this as a problem. I took the four screws out of the gate and undid the four latches holding it in place.
The gate had a number of lines of plastic for strengthening the shape of the gate. There was the center where four raises stopped and opened into the shape of a square. I noticed the blank spot was the about the size of a quarter. I grabbed one and put it in. It was juuust a little bit bigger than the quarter!.

So I pulled the quarter tight into one corner and used a ballpoint pen to draw a quarter circle (pun intended)
I did that for all four sides. You can see above the top right of the quarter there's still some space between the raised plastic.
I busted out the dremel with a round barrel sandpaper attachment and rough sanded until I got close to the lines.

 I got a small piece of 800 grit sandpaper and smoothed it out so there were no rough areas. I just used my eyes to judge the proximity to the line. I didnt want to sand away completely. I was just out a little further than the original Square gate's corners left off.

You can kinda still see them in that image. If you right click and hit view image it gets a little bit bigger. Anyone that opens their EX2 stick will see it first hand. The job looks a little uneven in the pic, but it's just the angle of the camera.

The stick still connects with the gate!

Now I have a Circular Gate, or an O Gate!!

As soon as I screwed back in the 10 screws I flipped the controller over and felt a HUGE difference. I'd say I can do 2 to 2.5 360 motions in the same time it took me to do 1 with the square gate. I have noticed my move times have changed. I have missed a few diagonal jumps, but it's the first day of the O gate. I can tell I'm going to become just as accurate with the new gate. I _Think_ I'd prefer an Octagon gate best, but this is MUCH better than a square gate!

All in all the mod probably took about 20 minutes. If I had a preset plan and all the tools ready I think it could be done in 15.