Re: spyder fenix wont fire
The high pressure may cause the marker to not recock, or even fire. Think about it this way, the front spring is pushing with so much force on the cupseal to keep the valve closed (usually about 2-5lbs). When you pressurize the marker, it has all that air flow to keep it closed as well, about 400psi. Volume is about... eh, I'll pull 2in^3 out of my ass. That means that on top of the 2-5lb spring, it has an additional 5.5lbs of force pushing on it [(400psi/144)*2in^3]. The main (striker) spring then has to open it, and if you aren't careful with how much pressure you're giving the valve then the striker won't be able to open the valve all the way. If it doesn't open all the way, then it doesn't have enough air coming out the rear to recock the marker fully, and symptoms can vary somewhere between full-on jackhammering and nothing.
I would turn the regulator completely off (keep in mind that you need to clear the pressure after the regulator is adjusted down to get a proper reading), then raise it until it works properly with the velocity adjuster (on the back of the bottom tube) screwed halfway in, or even a little less if desired. The way to turn off the regulator is to turn the set screw counter-clockwise until it is about flush with the surface of the regulator. Attach the air source and slowly turn the set screw in, until it sits at about 300psi. Wearing your paintball specific mask, cock the marker and take one dry fire shot. Continue this process, raising it 50psi at a time, until it works. Then turn the regulator up another 25psi, and ensure that it works consistently. When you get to the field, adjust your velocity adjuster to match the field's limit. If your velocity is too high, unscrew the velocity adjuster. Too low, screw it in.
In cold temperatures, I would definitely recommend an HPA tank over a CO2 tank. The HPA is not as susceptible to low temperatures as CO2 is by a long shot.