Joe,

As far as I know the only factory load 20 ga low pressure spreader option to the RST is the Poly Wad "Double Wide". I think it's only available in 3/4 oz # 8 & you would need to determine the suitability with Damascus bbls. It's a spreader version of their "Vintager" load.

I have no experience with it or the RST 20 ga Spreader.

I have used the std Poly Wad 20 ga spreader in a tightly choked Merkel on quail with good success but never did any patterning with it.