If it doesn't pressurize, it is generally an indication of bolt stick. Since your mag is original with the powertube spring, I suspect you need to install a powertube spacer that is longer than the spring you are using now. If you know someone who has a mag with a level 10 bolt, get one or two of his shims and use one at a time to see if they help.
Originally Posted by Chencho
A bad regulator seat oring will cause a high pressure in the front chamber which will result in a high velocity. Usually, the valve will vent air out the back when this happens.
I would change all of the orings as a start anyway so that you know what you are working with. Most mag problems are due to a bad oring.
Except for the Automag in front, its usually the man behind the equipment that counts.