AR-15 Bolt Ring / Gas Ring per MIL 8448511 – Top Quality U.S. Manufacture Packs
Available in packs of 3 or 9. Although buying quality components significantly decreases the probability of things breaking, its never a bad idea to keep a few spare parts, especially wear items like gas rings in your range bag just in case.
Verify gas ring condition by extending the bolt inside the BCG, Place the on the BCG face down on the bolt. If the BCG doesnt compress, your gas rings are fine. If it compresses, your gun will still run for a while, but consider changing your gas rings soon. And no, you dont need to stagger the gaps, they will rotate on their own as the gun cycles.