The 50-caliber Mark

So, I find it kinda weird that the whole "right to bear arms" has essentially an intrinsic limit. Indeed, it would seem the limit is the National Firearms Act of 1934. That act has had a mightily confusing history. There's also the Gun Control Act of 1968.
What is that limit?
The caliber of what is acceptable debate concerning allowable weapons seems to top out at about, well, 50 caliber. Above that one ends up with a "destructive device" which is illegal. New Jersey, which has fairly restrictive laws regarding firearms may be banning 50 caliber guns. Nobody ever gets killed with those things -- they're fairly uncommon. But NJ may be topping out at 49 caliber. (Shotguns are exempted.)

It just seems odd to me that no one really seems to object that their right to bear arms doesn't actually include weapons a militia does in fact use. Like grenade launchers, rocket launchers, that sort of thing.

The entire argument over gun in the US is limited by a shared fiction that "arms" seems to begin and end with guns of certain calibers, that do not have explosive projectiles. So what does this right to bear arms really mean? Who knows?
Well, whatever the courts decide it means is what it means I suppose.