When the bolt carrier and cam pin hit the bolt to start the rearward acceleration of the unlocked bolt it creates a very high acceleration load (perhaps 200,00 g’s) that gets transmitted to the extractor. The extractor bends like a spring under this load, but being a very brief impact load the extractor springs back to it’s original shape and springs away from the case. This dynamic motion causes the extractor to be out of position for the first .15 inches or so of case extraction. The only thing holding the case against the bolt face (while also keeping the ejector compressed) is the residual gas pressure in the bore. There is roughly 1,000 psi of gas pressure during initial case extraction.
The gymnasticator was used to duplicate the bolt and extractor dynamics without the bore pressure, just to provide additional evidence to verify this phenomenon.
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