Given that the gun is to protect me from the gov I do not think they shoot fast enough...

I want the old days where I could own a ship loaded up with some cannons...

Think for a moment that back when the founders wrote this yes all they had were muskets but individuals that had the money owned armed ships capable of destroying an entire city! If anything I feel like individually we have given up a lot of heavy firepower that we previously did have in the past. I do not think anyone today is allowed a weapon that can take out a city but back then such things could be found on privately owned ships.

Obviously today we do not want people running around with the ability to blow up a city and I do not think anyone is trying to allow for that but it is something to think about as to what sort of firepower the founders were allowing and were already present in their day.