A black magic reg should have the hose fitting into the side of the reg. The stock prostock reg has the hose threaded into the end.
For fitting in the side of a reg, keep the reg on the gun and use a proper sized wrench on the fittings.
For fittings into the end of a reg, you might have to use a well padded vise or wrench to hold the reg while you turn the fitting. I repeat WELL PADDED, you don't want to scratch it up.