Aeroprecision AR-10

[Rainman]

Recently I had a round jam in my AR-10. When I attempted to clear it, it was absolutely stuck. Essentially I had to strike the buttstock on the ground while pulling the charging handle back to clear it. When the round popped free, a silver ring also dropped out (see attached photos.) I am a relative newbie to this caliber rifle (had mainly been .22LR and .223 ) so I have no idea what this ring is for and how to proceed from here. I am concerned that trying to just load and fire this rifle and an issue occurring. Any ideas? TIA.

[Rainman]

The ring measurements: 0.810" external diameter, 0.620" internal diameter, and 0.140" at it's thickest point. It has a concave shape on one side and convex on the other.

[98Z5V]

That's a 5/8" muzzle device crush washer, right there.   I don't know why it would be inside the receivers, though. 

[Rainman]

Ahhh... that explains it. I took the muzzle brake off because I was afraid I would need to completely disassemble the upper and run a cleaning rod through. Thank you!