This is a very simple operation. My Op rod piston was toast as it had .009 clearance and the gun wouldn't cycle. I carefully drilled out the two Rosette Welds that hold the piston in the op rod.
The correct clearance is .004-.007. under the ID of the gas cylinder.
I then measured the piston which is nothing more than a piece of round stock with a spud turned on it. I turned the OD of the piston until it had .004 clearance in the gas tube, and then turned the spud until it fit into the hole in the op rod. Then I rosette welded it back in place.
Gun runs perfectly.
Anyone with a simple garage lathe and a welding torch can do this, or any local machine shop could do it for you. The new piston is worth $10 on a good day.
Randy