Fabien,
Glad to hear that you found an easier method to install a Luger mainspring.
I fought with my first mainspring a few months ago. I made an inquiry on this website about the tool that they used at the factory. Someone posted a photo of the factory tool and I made a copy.
I started with a $4 awl from Loweâ??s. I cut the tip off and ground about �¼ inch of the taper into a diameter that fit into the guide rod hole. Then I heated and bent it.
When I tried it I could not believe how much better it worked than the method that is recommended on this website. I literally had the spring out and back in within a minute or so with little to no struggle.
Here is a picture of the tool that I made.
Chris