The 20's for the big makers of paradoxes Holland and Westley, they were late guns. Westley's had a three groove ratchet style, I have never examined a Holland 20 but Holland changed the rifling on some of their 12s sometime after 1910 to a 9 groove still ratchet style but looked more conventional. Westley's shot the capped 425 bullet at 1500fps. I have heard Holland may have had two loadings for their 20s. You would think the Simson being made in the 30's would have been regulated for a readily available 20 bore paradox loading.
