Using iron sights on my m1a scout, distance from front sight to rear is 23", and assuming a perfect zero, how far off would impact be if my vertical sight alignment, front front to rear, was off by .05 ? 100 yards
You need to say at what distance?
In order to know how far off, we need to know how far down range.
However, as a second choice, the error can be stated in terms of MOA.
Calculating how far off is very simple but it's best if you know the distance to the target.