At the time there were limited arms (you took about 2 minutes to reload) vs able to empty a couple clips in that same amount of time, now.
There were also limited religions and limited forms of speach and press at the time too. Should the first amentment only allow freedom of religion for the religions that existed when it was written, or only apply to actual speach and hand written docuements? And I guess it should only apply to newspapers and town cryers, because TV, radio, and the internet did not exist when the bill of rights were originally written. Also, the regular people had more advanced wepons than the army did because rifles were not supplied to the troops, they only had muskets.
the point of the constitution is to address issues in fairness. Doesn't deal with everything, but it's the core basic point of the document.
The constitution has nothing to do with "fairness" it is about limitations on the federal government and the absolute rights of the people. The founding of the US was not about fairness but freedom. What we have today is the idea of fairness and that is why our society is messed up and why we alow our government to rape us with high taxes and expect the government to fullfill all our needs.