Oh, and a peep sight would easily allow 150+ yard shots with a little practice, as long as your eyesight is good (even with glasses).

In the Marine Corps, we shot at the 500 meter line with open peep sights (I was in before they started issuing the A4 uppers with various non-iron "sight systems" to anybody but SOCOM troops and a handful of MEU-SOC guys). With a good sling and shooting position it is quite do-able.

A little trick with peep sights is to use a lighter and black out the front sight with soot. Makes it a lot easier to see clearly and line up more precisely.

Mike