Is it just to prevent glare off the front lens giving away position for snipers and such or do they have some benefit to a target shooter?

Kill flash and lens caps prent the glare.  Sunshades (at least in bechrest rifles) help to tame the glare /mirage coming off the barrell.

n8

sunshade also helps if you are firing into the direction of the sun. Keeps the glare off the front glass.  more for keeping the sun from causing a bad sight picture than anything.

works similar to those that are in your vehicle




shades from the sun.




also helps keeping the heat mirage from the barrel out of the sight picture too.

Thanks for the replies guys.

Do I interpret correctly that if I shoot in the morning on an eastern facing range, a sun shade will make it easier to see the target clearly?

Will a 3 inch shade be adequate, or is 6 inches better? I have a DPMS upper with the full length free float hand guard, so I don't get a lot of heat mirage off the barrel.

A sunshade on a rifle-scope works in a similar manner to a lens shade on a camera.  The shade extends beyond the front objective lens and is sized in both diameter and length so as to not cause any "vignetting" or reduction of angle of view, but at the same time block any light outside the angle of acceptance of the scope.  This  helps the scope retain as much contrast as possible, prevents flare, and helps keep the image as crisp as possible.  It does also help reduce the flare or signature reflection that may be visible to others.  The shade offers flare protection to help maintain image brightness and contrast in addition to any flare reduction offered by coating the lens surfaces with anti-reflection coating.