You will likely want to use the lowest weight recoil spring. There were a number of different springs used in various models of Lugers. All this is involved in the balance of the action as it cycles.
Also double check to make sure that your extractor and the ejector are both clean and undamaged.
Marc
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 Igitur si vis pacem, para bellum -
- Therefore if you want peace, prepare for war.
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