Relief valve in piston

This plan allows for adjustment from exterior of gun.

I kinda/sorta believe such relief valve might work when incorporated in a a pumper with a flat top piston. This is inspite of inducing a bit of headspace into the system.

I suspect that one would not have to count strokes once the relief valve is set to desired fps of the gun via chrony. Thinking that the valve would simply bleed off even at mid stroke.