Just separate the upper and lower receivers, use a roll pin punch to push out the pin on the bolt catch/release. Make sure you are careful or the spring can pop out. Remove the spring, cut two full turns off of the end. Insert the spring with the cut end first, reinstall the bolt catch/release, insert the roll pin. Easy peasy!
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M&P40c/15-22/SD9VE/Mossy500
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