@WilliamLu, did you find a solution?
I have the same problem here, I'm trying to print in silicone but I can only push about 50 mm by hand then I load the cartridge in the Discov3ry and I can push maybe 50 mm more but it's impossible to extrude. I cannot even reach the middle of the tube.
@Charles_Mire, I tried several hardware store silicones and they are all the same: It says it dries in 10 minutes/24 hours for the middle. They stay fresh and liquid. I have had them in cartridges for days and they are still good, I just can't get them through the tubing. Would you have suggestions? Thanks.