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Spook - necking a cartridge from 20 cal to 30 cal is not an invention. It is done with every new cartridge. Even the 6.5 Grendal is already a 6mm and a 30 cal.
For the 300 AAC BLACKOUT we did not work from any existing drawing. We took a 221 Remington Fireball and used all base and taper dimensions from the Remington drawings. We then necked it to 30 cal, picked corner radii, and set the throat length so that a 220 grain Sierra would have a 0.010 jump to the rifling if loaded to magazine length. We kept the same headspace location as the 221 Fireball, but changed the diameter datum to ensure that the measurement would not be on a radius.
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R&D for AAC
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