AndyJ,the magazine spring retainer is captured on both types,the WingMaster and 1100's use the metal one that you use a screwdriver to pry out,it is only used to keep the spring flying out when cap is removed.The dimples in the cap and the detent ball on the barrel ring keep the cap tight.My Express has a plastic one that is removed by pushing down,past the little dents that have to be drilled out to put an extended magazine on,and rotated to allow to pop out.This plastic one serves to keep the spring from flying out when the cap is removed and to keep the cap from loosening on its own.It is much cheaper to make this setup than the one used on the WingMaster.But its disadvantages are having to drill or swage out the depressions in the mag tube if you wish to put an extension on(which I have no interest in)and in my case it does not seem to keep the magazine cap fom loosening up when it is shot a lot such as when shooting several rounds of skeet or a 100 round course of sporting clays.My 1100 never loosenened during use and my Ithaca 37,which also has a detent and dimple set up on its barrel retaining nut has never either.My Kuhnhausen shop manual shows the plastic mag spring retainer used on the 1100 special field model and 11/87 also,though it describes the 11/87's as being slightly longer.It calls the plastic spring retainer and matching cap late style.The metal spring retainer and the cap with the detent dimples are called early/intermediate style.