M-261 Manual Page number C-4 gives you a exploded view of your bolt.
This is part number 16.
This is a common wear item. Your unit can function without this spring but over time will damage your buffer so though you can continue to practice without this part, you should replace it if it breaks.
You can prolong the life of this spring by making sure your Position Spring Retaining Screw remains snug. You should check this screw when you clean your unit.
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