"Arms", "keep" and "bear" are terms of art used in legal and philosophical discussions that predate firearms and the colonization of this country. Majority brief on Heller has some information about this as do the Founder's notes and discussion, references to prior law, etc.
The essence of 2A is two-fold: you have only the rights you can defend and individuals have an inalienable right to self-defense against predation, small (local criminals) or large (government run amok).
The use of "arms" at the time clearly contemplates firearms but is not limited to them. Then, as now, the firearm is the most effective means for an individual to defend oneself, singly or in a group, depending on the circumstances. However, IMO the Founders did not intend to limit what means individuals chose for self-defense. Recall also that edged weapons played a large role in combat at the time.
When/if firearms become obsolete technically, 2A will be just as relevant a statement of the human condition as ever.
Watching Star Trek NG last night, and seeing the Borg become immune to phaser's of a certain wavelength, I counldn't help but wonder why no one mentioned kinetic weapons as a solution...In the situation, a 1911 might have been very useful.
Okay, it's early. I will go have some more coffee...