Funny how the time eras are kind of stitched together in this universe
The earliest Walther PP I know of was made in 1935
and they have an early steam engine car (closest I could find was the 1900 Cleveland Runabout, but I could be wrong) which was from 1899-1900
So if this manga takes place in the early stages of Shelock Holmes from the books, that would take place in 1880
Just a little history stuff lol, I know this is manga and the "rule of cool" is how things function so I won't berate so much because I generally love this story.
Was just funny because a previous chapter when the British commandos were storming a chateau, they had automatic rifles so I don't think the author cares so much about realism for his take of Sherlock.