Question for the string Guru's

[thumper]

My set up : Vortex-carbon express maxima arrows-rope cocker-varizone scope-100gr. tips-factory string and flemish string. Question, why does the factory string shoot alot more accurate than the flemish (gray and black)? At 50 yds the factory will drive tacks, groups open up to 3-4 inches with flemish. I even tried some of the goldtip laser II arows, everything shoots better with the slower factory string. Is there a reason for this. Also seem to be eating up servings, will get some 3000 grit automotive sandpaper and polish the claws tomorrow. Any answers or help would be greatly appreciated.