Has anyone ever actually seen an AR-10 bolt break a lug? I've personally never heard of it happening.

Those chonky .308 BCGs and bolts are pretty tough. I got a basic Toolcraft bcg and it just works.  I clp paste it pretty liberally before the range session and all the cargon wipes off with a rag.


I don't recall any stories of 308 bolts or BCGs breaking and I know a couple of guys at the range who shoot quite a bit of 308 and would likely have mentioned something, given how much they complain about tuning gas systems.  


That's just my anecdotal experience.

Very early in the development of the original AR10 there were a batch of Sudanese bolts that broke lugs, same with some extensions due to heat treating issues and the squareness of the lugs. The Portuguese version thus had very beefy lugs which were thinned a little during the development of the SR25. The design was mostly copied by the Arma-Ill bolt which actuakky has three patents on it and then finally the DPMS bolt style which has become the standard if there is such a thing in the AR10 family. I personally have not heard of a modern 308 AR bolt breaking lugs. HTH