The piston heads for the operating rods can be replaced. They will have to be silver soldered into place. The new piston will probably have to be fitted to the gas cylinder first to insure a proper fit. Too tight and it will destroy the gas, too loose and the rifle will not function. I have seen a number of M1icon rifles come back into the US where the gas cylinders were recovered and use with oversized piston heads. Some militaries did not have the luxury of new spare parts and recovered and recycled used parts to operational status.

--fjruple