Well my 306 carto's came today,they vape every bit as good as the 510's with aluminum threads,there is less filler so it doesn't take as much liquid to fill it.The only drawback I see so far is they are smaller in diameter so my 901 cart tip doesn't fit and too big for a 302 tip to fit over so it is metal in the mouth. how bout one of you mini users trying your carts to see if we can find one that will fit.preferably thin flat whistle tip.Appears to be 8mm opening.I got 3.4 ohms resistance on a wet one.For now I have cut the end of a condom or cover and am using it ,better but not a whistle tip.