I talked to a buddy of mine of a neighboring swat team and he said they got new M-4 types from DPMS and were having problems with the eotechs mounting on the rail, they keep coming loose and would not tighten down all the way, I have never heard about this.  Has anyone had any problem with out of spec rails or out of spec eotechs?

A bud of mine had a similar issue, probably a little over a year ago…

He is also LE & his place of purchase (rifle & optic) only complicated diagnosing problem.

In the end I think it was determined that his upper was out of spec. & it was replaced.

His rifle was DPMS also.
(Bad luck?  I’ve always been satisfied with my DPMS products… just wish they’d start shipping the metal mags for the LR308… hurry up already!)

I've had very good luck with DPMS.  With that being said, there have been numerous reports of bad QC on their part.  It's probably a bad batch of uppers.  If DPMS won't take them back, a very easy, albeit more expensive, cure is the Larue EOTech mount.  It also serves to give a better sight picture than with the optic simply mounted to the rail.