When the Constitution was written a well trained militiaman could load and fire his musket 2 or 3 times per minute. Obviously unsuitable for personal protection beyond a single shot before an attacker could close with a knife, its main use was in a battle line where many other similarly armed men would prove an effective deterrent to an advance. The muskets effectiveness as a hunting tool is equally suspect with its limited range, general unreliability and high cost to maintain and operate. Trapping was usually a better option.

Fantastically expensive, muskets were generally sourced from Europe or were assembled with foreign parts. Most Americans being farmers did not own muskets. Being a time before the US had a standing army, having a well regulated militia was deemed important for defense of the country and so the right of men to bear arms (in order to serve in the militia) was not to be infringed upon.

https://www.youtube.com/watch?v=SJMbxZ1k9NQ