The ss valve is the biggest improvement you can make to a prod peroid. David
Sorry, just read your newest post how it shoots well without the moderator. Make sure the air splitter o-ring is lubricated, I've heard that if this o-ring is unevenly lubed or dry it messes with the harmonics. Also try tightening the shroud to varying amounts, some people actually loosen it so it is backed off the breech by a hair, then you can try finger tightening, snug, and tight. I also wonder if a bent barrel could have harmonic issues with a shroud.