The flintlock was first invented during the Southern Song Dynasty in China. In 1132 AD, the military strategist of the Southern Song Dynasty invented a kind of tube-shaped firearm called the musket. It could be called the ancestor of modern tube-shaped firearms. In 1259, the Shouchun people created a type of gun, which was the real origin of modern shotguns. Therefore, the musket was first made between 1132 and 1259.
The making of the Christmas story occurred at a certain point in time. Unfortunately, I don't have that information readily available. You might be able to find out by consulting reliable sources like film archives or entertainment news.