Last fall I made a small ELB for my wife. I made it out of an Ipé board and aimed at ~45#@28", it finally turned out 43#, but I believe that if you dared to draw it to 31" you'd get about 48#.
Picture of the stave bending before fitting the hornsSo here is my recipe and result:
Total length: 74", ntn 70". Round section from the horns and 3" towards the handle, after this a rather "pointy" D-section all the way down to the handle, which has a more round D-section.
Measurements width/depth [mm] at different distances ["] measured from the lower horn:
10/11@0", 15/13@8", 19/15@16", 22/17@24", 25/20@32", handle ~25/21 for 4", 25/20@36", 22/17@44", 19/16@52", 15/14@60", 12/12@68", 11/11@70".
(Sorry about the mm, but just divide the mm-number with 25,4 and you'll get the measurement in inches instead)
Total weight: 470 grams
Set, after ~150 arrows: 1¼"
Arrow speed with 10 grain/pound: ~155 fps
If you made a similar bow, with either a more rounded D-section or just one mm more depth, I assume you'd hit your desired weight of 50#@31".
Cheers,
Ola