is that a Mcfarland ring? crazy it could fail like that. Did it lockup in battery?
Out of curiousity, what ammo were you shooting?
If it didn't mess up your carrier I have a spare bolt you could use.
Is it under warranty? Seems like the carrier would be the culprit. But it could be the bolt too.
From what I've found out, the Magpul MBUS' are meant to be mounted to a rail system. Supposedly, the materials used in the construction aren't meant to stand up to the heat generated at the gas block. By looking at the height difference between a standard railed gas block and the rail height gas block, I'm not too sure that the extended front site post would still be tall enough???