Basically, it looks like the existing 35mm Bushmaster ammo has a case that is 50mm at the base, and necked down to 35mm. Which, if you remove the shoulder, and leave the case at 50mm, means you only need to change the barrel and breech, and the feed rotors, to turn it into a 50mm gun. Those are actually changes you can make in the field. I’ve seen references to Oerlikon doing the same thing with their 35mm autocannon.
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