Quote Originally Posted by Shed tuner View Post
I was also wondering if the cup face provides more cushioning for the final piston landing, due to physical compression of the seal at the perimeter...
I agree with this, especially with leather washers after finding lots of damaged piston screws where the washer breaks down over time to a point that the washer has started to lose its sealing effect and the piston slams harder against the end of the cylinder. With a bit more washer in front of the piston and a inner washer that recesses the piston screw there is less damage.