Lee, My S4 started chewing up the string serving that feeds into the cam. Turns out I had a little bur in the cam groove. I found it with a q-tip then a little very fine sandpaper fixed it out nice. I do know that the large refers to the medium-long draw mods and the small are the short-medium draw mods. The S4 has like 6in of draw length adjustment. I do not have an answer on the poundage.