Hey Eddie,the rubber may tend to grab the bg barrel tube and slow down your dart or throw off your accuracy. You maybe better off spraying your paper cones with a clear lacquer this would harden them and make them semi water resistant. Just a suggestion but we all learn from experimenting. Have fun blowguning !!
That Phil Swift guy that does the Flex Seal commercials has an unlimited supply of that stuff. Might be just as cheap to dip them in gold or platinum. Just sayin'. Raptor is probably right about it being "grabby" though. Look up Backyard Bowyer on YouTube. He shows how to make cones out of duct tape, with one piece outside-in wrapped with a piece around the outside regular way so you don't end up with any sticky side exposed. Those work pretty well. No sticky exposed that would collect all manner of nasty, and they are "slick" enough that they don't grab down the bore of the gun. Plus they are waterproof.