Congress defines most every able body male as part of the unorganized militia and there is no public armory for them to store their arms (this only available to organized militia) at or use leaving only a private armory (consistent with historical at time of founding where private persons stored their militia weapon at home), so I'm not sure it makes much difference in practice whether the right ascribed to the people be connected to being a militia servicemember or not for the purposes of the example of owning a select fire infantry weapon.

Probably the main effect is to grant women and the more elderly the right to bear arms as well.

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>Congress defines… historical precedent… but we were talking about a plain-text reading of the Constitution.

That makes it easy then.

The plain text ascribes the right to the people not the militia so it's moot whether they're in the militia or not in such case to have the right to keep and bear arms.