So does the coefficiant of friction of dart cones affect the dart speed?
I have personally found that tyvek, which is very slick, along with a well-polished and teflon-dry-lube coated steel blowgun... is much faster than a PVC blowgun of the same caliber(uncoated) and duct tape darts.
Just something I noted. It seems to me that the lower the COEF of the materials of the darts and bore... the faster the dart.
Also noting that harder materials have lower COEFs and smoother bores have lower COEFs.
Also, keep in mind the need to maintain a seal.