Smooth-On is pretty gooey for syringes.
I use the 3oz cups as well. I had a riser that I glued up and it dried slow. I assume I mixed wrong but it did eventually harden and is holding with no issues so far.
If I slow down a bit its easy to mix correctly but it seems I'm gluing up when I have 4 other places I should be or its late. Such is life with family, work, and hunting.