Found my answer for pressure:
Heres what I've got: (Trying to calculate whether its possible to use gbbs)
Use HFC134a guns will be considered as required 80psi to work, where as propane gun is 130psi. This brings the solution...
HFC134a: Use Propane around 0-5 degrees
Propane: USe Propylene approx 5-10 degrees...
Any daredevil want to try? (FYI Propylene is extremely volatile)