The claims in the Scientific American article for the shotgun is blatantly based on imagination. And various of the claims mentioned in later newspaper articles is stretching the imagination to say the least.

That the shotgun was effective is undoubtedly so. However, if it was that good we would have seen hundreds if not thousands of the shotguns in surplus, as well as whole battalions issued with them. Nobody assaults a position with a shotgun, many might use it in defence, close quarters combat, house clearing, etc. Even there high capacity rifle or SMGs are the norm.