This question has been debated ad nauseum on this and other Forums. What is often cited as Gospal is Sherman Bell's writings in the DGJ. As a Degreed Engineer with Graduate study and research in Metalurgy, I have found Bell's articles to be superficial in content and approach as well as potentially dangerous for others to use his results to justify thier use of shells for which a shotgun was not chambered. When an item is manufactured, it is engineered for a specific set of requirements. To change those requirements is folly when dealing with shotgun chambers. I will not debate this again but simply note that there is at least one person with academic credentials that does not agree with Bell. EOT-Dick