zeroing problems

[fng13]

I just purchased a 1" Burris P.E.P.R. mount and a 4-16x-42sf Nikon Monarch scope combination for my ar-15. I took it to the range today to zero it. At 25 yards I got an almost correct zero but I used all of the right adjustment. The mount is one peice so I am unsure how I would have got it out of alignment. I was careful to tighten the the rings down equally. After levelling the scope, I snuged up the rings before using 5 in/lbs on the front ring first then moved to the back ring. I then repeated this to 10 in/lbs. I suppose I could have mounted the entire mount incorrectly somehow by overtightening it, but I only hand tightened the mount screws.

Anyone have any suggestions or may have experienced this?

thanks,

Fng13