It will be for my FN Mauser 98 .275 Rigby project as a back up in case of a scope failure in the field, but only if I can get positive feedback about them from people who have used one.

Tophet1 you could do to have a look at this style as it is simply wound down for scope use. If you are looking at a 275 Rigby this style of sight is more apropriate than a bridge mounted unit and gives an extra 3 in of sight radius.

http://i667.photobucket.com/albums/vv39/VonGruff/7x57StalkingRifle02-02-09021.jpg

Von Gruff.