How much of a difference in accuracy at various distances is there when using a scope mounted on top of the carry handle, as opposed to on ultra-low rings on a flat top? Also, while using a scope on a flat top, does the front sight block the view and if so how severely?

This is all a matter of where the line of sight intersects the bullet trajectory (which is influenced by bullet weight, speed [barrel length, powder charge], etc.).  The "accuracy" of said rifle does not change....period, only where your crosshairs will line up with the bullet trajectory.

Basically, as you raise your scope higher...your bullet will hit lower up close, and higher out past your "zero"....then proceed to drop back down into your "zero" and continue down from there.  With the scope nearer the barrel...your bullet will hit closer to your "zero" up close, and closer to your "zero" out past your "zero"....but it will also drop off faster after your "zero".  Either way, the bullet follows the same path.

If you know your bullet's trajectory...either can be used successfully.

Max

While the above comments are true, the main problem with having your scope mounted "way-up there" on your carry handle is [b]consistent cheek to stock placement[/b], this results in inconsistent shot placement and makes your rifle harder to zero. The lower flat top scope mounts place the scope at a height more similar to your standard bolt rifle, thereby improving your ability to obtain a moer consistent cheek to stock placement.

As to your second question, NO, unless your are using a 4x scope or less the most you will ever see of the FSB [b]might[/b] be a shadow, but as your eye is focused on the target, one will NOT see the FSB.

Mike

Higher scope mounts will also magnify the effects of canting the gun.