I installed a pair of Magpul MBUS flip up sights on a 308 AR with a high-profile receiver/handguard. I had to run the adjustment all the way down to get them to zero. Is this normal since they are normally used on 5.56 height upper?

Yes.

Hopefully my quick MS Paint helps the understanding. Black = bore line. Greens are different rail heights. Yellows are the sight heights, with the rear being fixed.

Attached File

Thanks for taking the time to explain it!

At what distance did you zero at?

This ^^^

Also, is the receiver rail and the handguard rail equal height?

50 yards and yes receiver and rail equal height.

That may be due to variances in your particular barrel and/or handguard as much as anything because the zero settings on your sights should be more or less identical if the only variable changing is 1/8 inch or so in height of the surface they’re mounted to (as long as the height of that surface is varied identically front and rear). Basically what I’m saying is that if I could put a perfectly uniform 1/8 inch height spacer underneath the front and rear mbus sights on my AR there would be minimal (maybe none?) change in the zero. That’s assuming the only variable changed was their height.

Agree, rail height shouldn't matter, as long as the rails are equal height and parallel.  I would put a straight edge on the top rails to make sure that there isn't some slope in the handguard.