Dictionary.com Wrote:bear arms,
a.
to carry weapons.
b.
to serve as a member of the military or of contending forces.
A grenade isn't a weapon, it's an explosive. A stick of TNT isn't a weapon, it's an explosive. A can of Coke isn't a weapon, it's an explosive [albeit a weak one that will only really hurt if it hits you directly on the head, at which point it becomes a thrown missile, which is a weapon].