....the piston being so thin in diameter to be able to fit inside what is now a very small diameter tube inside the arbor pin, would that piston be too thin and delicate to stand up to the stress of operation of it flying back to push against and cock the hammer?
That also occurred to me. The piston would end up being about the size of a finishing nail and what I remember about those is how easy it was to bend them. It's going to require pretty good support. I don't know how much it will matter that as the piston pushes on the hammer, it also has to slide a bit along the inside face of the hammer strut (excuse me if my terminology is off).
Just going by holding a cheap micrometer alongside the hammer and going from full down to full cock on my SAA clone, it would seem that the piston is going to have to both push back roughly 1.2" and slide about a quarter of an inch along the hammer, and it's going to be doing that at some speed/force. (The distances may be different for a Remington `58, but probably not by that much. ) Seems like a lot to expect a small-diameter pin to do.
I also wonder how many shots the piston will be good for, given that BP can be kind of nasty stuff. There are a number of little clearances in Aki's concept. If the piston cruds up somewhere along its length of travel, then the weapon is out of commission until it can be torn down. And if scratches build up along the surfaces of the piston and cylinder, would it then foul even faster? Or is it possible to design the gas face of the piston so that it tends to self-clean the inside of the gas cylinder?
(I don't know anything about machining stuff.)