I'm well aware that Kimetsu no Yaiba takes place during the Taisho era, which is from 1912 to 1926. During this era, guns are relatively new to Japan, and from my understanding, they were considered too harsh for the public, and as such were prohibited (though police officers were starting to equip pistols and rifles around this time).
Now, it's made very transparent that the Demon Slayer Corps is not an official governmental agency:
There are hundreds of Demon Slayers within the organization, however, they are not officially recognized by the government.
This implies that Demon Slayers would not be permitted to use guns, yet in the manga, we get our first exposure to guns being utilized by a Demon Slayer...
... in volume 13, chapter 107, when Genya uses his Nichirin Shotgun against Sekido and Karaku.
With that being said, I've only made it to volume 14 so far and my searches on the web have yielded no results.
Is it ever explained in the manga, whether directly or indirectly, when a demon slayer may or may not use specific weapons such as guns?
Please be sure to use spoiler tags in your answer where applicable.