Hi,
I have do my homework and here are my result. I follow your tutoriel but I change the chemical product.
First, I use SuperClean. Not very good, remove some Krylon paint and a little bit of factory paint but you need to work alot. Some picture of the result:
Second, I use Lacquer Thinner. Very good! It remove Krylon paint very easily (I drop some Thinner on the toothbrush and brush the barrel, the paint was remove).
For factory paint I was only easy :P I let the barrel in the Lacquer Thinner 5-6 minutes each sides. After that I follow the tutorial.
One thing, the product don't remove orange paint, I need to sandpaper it
Some picture of my barrel after the Lacquer Thinner and the sandpaper (for remove some little paint spot and have a better finish):
I'm pretty happy, I will know what to do next time
PS: Use the Lacquer Thinner outside or in your garage cause it's smell very very bad.