I thought about trying o-rings for a single test firing and I may still try it tonight. It might demonstrate to me if the tighter piston I am making will do the trick or I need a bigger gas port. The o-ring ought to hold up for one shot at least!
I am working on the tighter gas piston because I would need to buy more aircraft extension drill bits (12" long) at $3.00 each to enlarge the gas port. The gas block is so close to the rear sight block that the drill chuck hits the rear sight block even with 6" long drill bits.