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  1. HK MR556A1 Backplate spring and locking pin question

    HK416 and HK417 HQ
    I am a new owner of a HK MR556A1 and recently installed a new backplate sling attachment. In doing so, I lost the pressure spring and locking pin (Owners Manual parts: 83.) Stop pin for locking pin Part #233115 84.) Pressure spring Part #233116. What is the purpose of these two parts and...