People in regulated militias should be allowed to have arms, by the technology of the 18 C. Seems obvious what it means.
Even if true, that does not mean people are limited to those weapons. The Constitution limits what government can do, it does not dictate it. Congress and the state legislatures determine what gun regulations they want.
Nothing prevents them from allowing fully automatic weapons or grenades. Until 2010 states could prohibit firearm ownership.