[quote=“AKMS”]Thank you for the explanation, and I understand what you described, but I still do not understand the need for the step in the chamber. I do not understand how, in a properly headspaced chamber, a cartridge can be “over-rammed” to the point where the cartridge is not held by the extractor. There are many, many rifles and machineguns using a spring plunger ejector that do not suffer from this problem. There must be more to the design of the StGw-57 that causes this to happen. Does it fire on automatic using some variation of advanced primer ignition? Does the fluted chamber have any relation to the “over-ramming” problem?
I agree that other MG’s manage without a stepped chamber but many of these use other means such as a short headspace which is not so obvious. The headspace gauges for some MG’s are a few thou’ shorter than the equivalent bolt actioned rifle. The Belgian MAG has a short chamber, if you pull the trigger on a dummy and then eject it you will find that the shoulder has been set back a little. Put that dummy back into belt links and pull the trigger on it again and 50% at least will not extract because the pressure of the ejector plunger combined with the extractor spring has shortened it further. These dummies are now scrap. This applies to the 35x228mm Oerlikon due to the velocity or ramming and the UK built 20x110mm Hispano guns. I suppose it depends very much on the feed system, if the rim of the cartridge is neatly slid behind the extractor claw before the round is stopped by the chamber shoulder then rounds will not be crushed. There will be more learned men out there who can explain it better, I am mainly going by my own experience (and mistakes).