I haven't watched many RU-vid videos for a while now due to travelling and general busyness; but the nostalgic smile that came to my face when you said "Ain't never been sniffed" goes to show how much I enjoy yours. This is a very nifty kit, thanks for showing it off Cap!
I think the foam seal might be rolling in when primed after loading. The vacuum seal you mentioned feeling. Maybe a longer top hat in the seal, I'll test. Better to prime them load. Yours came out looking great, nice cuts.
I just got a handful of fates from ollie's for $5 apiece for me and the family to bother each other with inside, thinking they were like jolts. Boy was I surprised when we tried them out!
I moded my rival fate by gluing a pvc tube into the plunger tube. I also made a BOOMco adapter and an adapter for 5 cm homemade grenades. Adapters are also homemade and they simply screw on some thing with threads on the end (don't know how it's called) which I attached to the end of a barrel. Using x-shot insanity darts I get ranges of 115 feet flat in average, using BOOMco darts I get ranges of 55 feet flat and using homemade 5 cm grenades I get ranges of 38 feet flat. I think the seal is also pretty good because it vacuum loads darts