How to change Luger Main spring?

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When an empty cartridge is extracted but not ejected and is caught between the breechblock and the chamber and projects above the breechblock that is called a 'stovepipe' malfunction. In my opinion a too-strong mainspring may contribute to 'stovepipe' due to the action not fully cycling. That malfunction would not normally be caused by a too-weak mainspring.

In your first post, you say you want to change the mainspring because you 'have to cover my slide when reloading by hand". I don't understand what you mean, could you describe whatever the pistol is doing more clearly?

Before changing the mainspring consider performing a tape test, which can be found by searching the forums. The tape test will give useful information for evaluating mainspring performance.