There's such thing as markup-tolerance. Blp weapons are less markup tolerant, since they have higher decay compared to laser ones. This means that higher % kills weapon's eco pretty quickly to a point that it even becomes less economic than the unlimited versions. Looking at the current prices, i can say that L laser weapons would be a more eco to go, breer p2a/breer p3a/korss380/korss400 for handguns and breer series for rifles. You can check economy of almost every weapon using this calculator:
http://www.entropiatools.com/avgdmgpec.php