You can make a pretty good argument that an *atom bomb* is not a *weapon* per se but a form of ammunition, some types of which can indeed be limited by treaty or law as inappropriate for militia usage.
Militia units and individuals might thereby have the means to deliver such ammunition, via aircraft, missile or some light artillery launchers, but their ammunition therefor would be limited to conventional warheads, unless some very drastic circumstances required otherwise.
Neither is the cost and proper maintenance of nuclear ordnance inconsiderable.
Well put. -- I think we all can agree that C-N-B weapons should be reasonably regulated.
-- In fact as you indicated, some types of small arms ammunition have even been limited in the past by treaty or law as inappropriate for military usage. But seeing that those days seem to be gone, 'we the unorganized militia' should not be limited by rules that no longer apply to gov't troops.