Posted: 7/14/2012 11:17:56 AM EDT
What O ring are you talking about,
The only O ring is around the extractor spring on the bolt, and should not make a difference it dry assembly (will have problems with extraction of live spent rounds through).
Low down is the bolt goes back together pretty much the same as any other AR rifle (with the O ring around the extractor spring), Bolt get loaded into the front of the carrier, cam gets loaded to retain the bolt, FP with spring gets loaded to retain the cam, then FP retainer gets installed to retain the FP.
Did you forget to install the FP retainer, and the FP dropped out the back of the BC, which allowed the cam rotated and why you can not get the bolt to unlock instead?