Found this video review/comment on the homemade blunder-bust that PM Abe's assassin used.
It reminds me of some homemade toys I witnessed in VN and other primitive cultures.
Not a lot of detail but it does show that someone that is committed can produce a weapon with very little "modern technology"
Based on the size of the barrels, I think it fired some sort of buckshot load?
https://www.youtube.com/watch?v=bdqufrO30mE
PS: The author Mark Serbu is of the Clan Serbu that manufactures the Serbu 50 line of BIG BANG rifles. At one time long ago I had the Bad-Jones for one of these :]
https://serbu.com/