Character mistake: In a shot that flashes by very briefly, a London newspaper's headline is shown: "Sherlock Holmes Aides Police." "Aides" should be "aids".
Character mistake: In the scene showing the outside of the hotel the British flag is flying upside down. The wider white band on the white X has to be top left next to the top of the flag pole. It is at the bottom, which is a universal distress sign.
Character mistake: When Holmes is being chased through the boatyard by the giant, he trips over the ship's mooring chain. The links are over a foot long, and should weigh 100 pounds each, yet the whole chain jiggles like it's made of Styrofoam.
Character mistake: Near the start, Sherlock reads a newspaper dated Friday November 13th 1890 - that day was actually a Thursday. About an hour later he reads another newspaper dated Friday November 19th 1891. If a week had gone by it should have read the 20th - a year could have gone by, but that date was again a Thursday.
Answer: The gun was modified to where it would not fire a bullet. It remained in the barrel.
MasterOfAll