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Unread 03-31-2012, 09:57 AM   #17
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The tape test is indeed performed at the rear of the frame, not in the toggle area (although it is a nice test to check the 'balance' of both toggle knobs. If one is out of sync with the other, it will cause the gun to shoot slighly to the left or right, depending on the knob.

Matching the knobs to the frame is critical for accuracy, and Mauser got their new Parabellum parts tolerances to such a high degree that they only had to match the rear toggle with the frame/receiver. That is the reason why on the MP only the rear toggle part has part of the serial number engraved on it.

But back to the test. If the main spring is to weak to slow the toggle down, or the ammunition is too spicy (fast burning powders or too much powder), the toggle will flex past it's stopping point, leaving a clearer marking on the rear of the frame. This is checked with the 'tape test'. It shows how hard the rear end of the toggle hits the frame.

The initial powders developed for the Parabellum pistol were basically rifle powders and had a slower burning rate than the modern pistol powders. This produces a different pressure curve, which produces different recoil characteristics.

The shape and location of the frame ear curves have been altered a number of times. The Swiss especially experimented heavily with the curve shape, and the 06/29 shape was tuned to that particular pistol, barrel length, spring and ammunition. Mauser, who based their 1970s design on the 06/29 found that the Swiss curve was ideal for the 06/29 but gave difficulties with other barrel lenghts and calibres. They eventually moved the Swiss curve a few millimeters to the rear in order to avoid further recoil issues.
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