Hinge pin isn’t serviceable. The 400, 500, 600, 700 all have solid pins. The pins are for the cocking levers and I believe the second set is for the ejector trips.
I might be going out on a limb here, but the only serviceable hinge pins that I can remember were found on a FEW W&S 700 actions when H&H acquired the company and they built the Bowood & Northwood model, and not all of those models were built on that unique hinge pin action. The actions made with a removable hing pin are pretty rare birds.
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