I just had a bolt break on a 16” carbine I put together about 5 years ago.  It has somewhere between 3000 to 4000 rounds through it.  The bolt broke across the cam pin hole.  Not the carrier only the bolt. I have not seen this happen before. The upper was put together by M&A.  Has anyone else had this happen?  It has had a suppressor mounted on it a few times, only a 100 or so rounds top.  It has shot mostly milsurp and wolf  55 and 62 grain.  Other than that I do not recall anything else that has happened to it. At the time it broke I was shooting wolf.

Your bolt was produced/heat treated incorrectly.

Get M&A on the phone and they will replace the defective bolt for free.

Or put your faith in a CMT MP Tested,I did.

You mean it wasn't a DPMS bolt?

My bolt is broke too,  just bought it off my buddy.
i bought a beta-c the same day!
failed to extract from chamber.
bolt hold open was jammed, open.
took some doing to unjam everything.
mine is really just cracked right through on one
side, and halfway cracked through the other.
probably , one more clip, and it would have broke.
makes me want to unload the whole lot of junk.