When you release the Sig Pro's slide from the fully-rear position, be sure not to "ride" it with your hand. My Sig Pro, when brand new, did this only when "riding" the slide, but never did this when allowing it to go forward with full force, or when shooting at the range. Because my Sig Pro has never malfunctioned, I was thus unconcerned, and attributed this issue to the break-in period. See FAQ X-2 for more information about the break-in period of Sig Pros.
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