[Dfariswheel]

Yes it pushes the cylinder back where it should be.

The S&W end shake is limited by the end of the yoke barrel seating inside the rear of the cylinder.
End shake is when the yoke shaft gets battered shorter, and/or the inside of the cylinder gets impacted "deeper".
This allows the cylinder to move fore and aft in the frame.

Putting a washer inside the cylinder restores the length of the shaft and/or the inside rear of the cylinder to factory dimensions.
If the gun had too tight a barrel/cylinder gap to start with, repairing end shake will put it back too narrow.
If the gun had a too wide barrel/cylinder gap, it still will after the end shake is repaired.

In other words, repairing end shake will not cause excess barrel/cylinder gap. Barrel/cylinder gap is a moot point when the gun has end shake.
Barrel/cylinder gap is not really an issue since this is determined only in a gun that's in proper order and has no end shake.
When the gun has end shake, barrel/cylinder gap opens when the cylinder recoils to the rear and closes when the cylinder bounces off the rear of the frame and moves forward.