Hi Tom,
Since Switzerland only used their own .30 luger ammunition, they had the time and the possibility to tweak the design to match their ammunition. It did come back to haunt them when they tried to introduce the 9mm round. They had quite a few problems getting the 9mm to perform reliably and accurately in their M1929 pistols.
Mauser eventually solved the issue by moving the Swiss curve about a mm to the rear, so the guns repeated properly with different barrel lengths and different calibers (.30 luger and 9mm).
This opening curve problem was the reason that Mauser initially only offered the new Parabellum in 4" 9mm and 6" .30 luger. The rest was too unreliable and they had already produced a large quantity of frames they didn't want to scrap either.
So in the Mauser parabellum design you will also find 2 styles of frame ears. The older 'Swiss' type and the newer Swiss curve, 1mm to the rear.
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