One of possible interpretations, which AFAIK was even on the books in some state for a time, was that second amendment meant compulsory obligation for each voter to buy, out of their own money, a military rifle and stand for militia training periodically - essentially, mandatory militia service.
Lots of ways to wring hands about a very badly written amendment.
IIRC, you need private gun ownership to have a militia (as the founders understood them). I believe the idea was regular citizens would organize when needed and bring their own guns.