I hope you didn"t buy it yet. I bought an M4 upper and used a red dot on it. I found I had a wandering zero when compared to buis sights. I finally found the problem when I retrieved my rifle from a rack at the range when it separated from the receiver. Aparently the GLUE holding the barrell and receiver together parted company. I reglued it and accuracy didn't show improvement. I sold it to a friend at a loss with full disclosure. I wouldn't touch anything they make. roups were 3" @ 25 yds benchrested. Hope this helps with your decision.