[lsllc]

You got really lucky! In MA possession of ammunition without a (MA issued) permit is a crime with up to 2 years in jail.

MA doesn't have ANY reciprocity with other states regarding your CCW and the City of Boston in particular has a ban on any high-capacity (>10 rounds) magazines of ANY sort/age. MA banned hi-capacity mags but only ones made after 1994, pre-ban ones are ok, just not in Boston (and I think a few other towns).

You are right about peaceable journey, but I would not risk any of my liberty or rights on the good nature of a LEO in such a state.