The author is obviously a huge fanatic of military equipment to the point of obsessive. There is no way that a person with little gun experience would refer to a gun as a Glock 17. And the author obviously isn’t ex-military as he refers to the cartridge for the bullets as a magazine, even to state saying it was a clip is wrong.
But the biggest issue is the lack of research into the Maunder Minimum. Yes it froze for longer during the year in areas prone to freeze, but it didn’t freeze the whole year. There were colder winters for a tad longer. It didn’t go from sunny on a lake to a frozen wasteland in 2 days. People starved and died due to lack of proper heating, insulation, green houses, the Black Plague, etc. I can’t even finish this book.