YES I have already searched and not found a thread about my specific issue.
16" HBAR chrome lined
Specter gas block
rifle length YHM FF tube
Phantom Flash Hider
YHM Flip up front sight MOUNTED ON THE FF tube rail
YHM rear BUIS
1st time at the range mechanical zero was hitting 10-12" to the right (harris bipod sandbag in the rear). Just about out of windage to get on target.
I read all the threads I could find regaring barrel indexing slanted FSB's etc.
I have no FSB but i figured perhaps the FF tube was canted or something
My EoTech came in last week I hoped this would help me solve the problem.
mounted the EoTech on the reciever did an old school bore sight and went to the range.
results were almost identical to the iron sights 10-12" off to the right again using a harris bipod and a sandbag under the stock.
when I got the EoTech zeroed it exactly matched the BUIS's cowitness.
So where does the problem lie?
barrel/reciever interface not true?
Could very well be that your free-float tube is a tad off center. But, since you say the EOTech was off exactly the same as the BUIS I would suspect an out-of-spec upper receiver rail perhaps.