I'd have thought way weak, but my form never agrees with the charts, so what do I know! I got some 600's to try with a set of lighter (45#@ my 28.5"draw)ILF limbs and they showed weak @ 29" length all the way down to 100gr. points. The 30" 500's w/175 gr heads flew best, but they're what I use with my 48-49# limbs, so they shouldn't work! I was interested in building a hunting shaft with 500's using Jason (Lb_hntr)method of double inserting to get a total weight and FOC bump at the same time, until I found out he does it by choosing 3 spines, full length, and picking components to give him weight/FOC he's after and trimming tiny increments at a time until he has a winner. I'm sorry, I don't have enough time left on earth to get there by "trial and error"...I'll drop dead cutting shafts, lol! Until then, I have a normal, low FOC shaft that flies perfectly and kills deer. When someone develops a chart that can tell me how much length/weight I need to offset the stiffening effect of double inserting then I'll give it another try...if I'm not dead!