I saw the warning, too, but wound up turning a PVC block that screws onto the barrel and presses an O-ring up against the barrel shoulder at the chamber end. It has a metal vent tube that stays above the top of the tank to allow expanding air to equalize its pressure and doubles as a hanger hook. I didn't want the chamber or feed ramp Parkerized, either.
For a Mauser barrel you just get a neoprene chemist's stopper with a hole in the middle and put a piece of tubing in it. A PVC double hose barb from Autozone or a Nylon one from Lowe's pushed into the stopper and engaged on the other side by a length of rubber automotive vacuum tubing that goes out over the top of the tank will let pressure equalize. You can bend it 90° or keep it short and extend it with . Personally, I prefer to heat and bend a steel tube so you can use it as a hanger, somewhat analogous to what Jim suggested.
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Last edited by Unclenick; February 19, 2009 at 02:15 PM.