http://www.texasarchery.org/Documents/AMO/AMOStandards.pdf

AMO stands for Archery Merchants and Manufacturer's Organization. It goes by a different name now (can't remember off hand), but the above link will give you some info.

AMO specs for strings actually are the same for longbows and recurves--3" shorter (under tension--150#, I think)than the AMO bow length. The catch is that is only good if the bowyer/manufacturer followed AMO specs when designing the bow. It will also vary with the material and number of strands used. A 12 strand dacron string is going to stretch more under tension than a 12 strand Dynaflight '97.

Most older recurves do get a string 4" shorter, but it can vary. Some (all?) old Herter's recurves get a string 6" shorter. I've seen recurves get strings from 2.5" shorter to 6" shorter than the AMO, longbows 1.5" to 4" shorter.

It's also going to vary depending on your preferances--I've seen some folks with 1" or more difference in brace height with the same bow--one likes it low, the other likes it high.

I learned some time ago not to rely on the AMO bow length. It's a starting point, but depending on the bow it may or may not give you the right idea for the string length.

Chad