Replacement Pistons For Weihrauch HW55

[T 20]

So would the heavier 50 piston need a thicker gauge spring to power a 55!. Mach 1.5

I think the HW50 piston is about 200gm at standard 65mm stroke, same as the b2 piston's weight, Paul.

I'd be inclined to go with the standard sized Weihrauch 20mm OD HW50 spring with 3mm wire as this leaves a 2mm thick wall on the spring guide.
I think my custom 50/99 uses a 19mm OD spring with 3mm wire.