arms are weapons.
That includes knives, swords, axes, halberds, pikes, bows and crossbows and not just firearms. In my opinion it includes much more than what I just listed.
arms are military weapons.
Weapons used in war.
Not sporting weapons such as a skeet shotgun.
Once you whittle the 2nd amendment down to the point that only sporting firearms are allowed than you enter into a legal trap.