Granted the vast majority of heavy hunting loads come with high brass but it's whats inside that counts.The plastic hull's interior design,wad,primer,powder,and shot weight determine the velocity.Brass height has no influence on performance.As skb pointed out the brass isn't even needed.There was a company-Rainell Active or something like that which made all plastic shotshells.They were very high quality but are no longer available.I'm not sure if it was price,availability or that folks just didn't accept the idea of all plastic shells or what but they're gone.