The so called assisted opener like the Cogswell and Harrison ,were not aclualy any thing of the sort. It is simplly that the ejector springs behind the extrators are pushing the extractors out rather as with many modern O/U s ,thus pushing against the face and appering to asssist with opening . When the gun is fired the extractors are held back so there is no spring pressure and thus there is no assist.
Self openers are generaly Purdey ,Boss ,Lancster wrist breaker and twelve /twenty's [others made similar] Churchill {Baker}and the box lock self opener {Smith's] made by Churchill ,Rosson and others . There are a couple of others that have been produced but they are lagely variations on a theme and produced in only small numbers.
