Holmes & Watson is a 2018 American-Canadian mystery comedy directed by Etan Cohen and starring Will Ferrell as Sherlock Holmes and John C. Reilly as Dr. Watson. This incredibly non-canon version of the adventures of Holmes and Watson was nominated for six Golden Raspberry Award (2019) and won four of them, for Worst Picture, Worst Director, Worst Supporting Actor, and Worst Prequel, Remake, Rip-off or Sequel.
In several scenes Dr. Watson (John C. Reilly) uses a pair of Webley .455 pre-Mk VI revolvers that are most likely Mk IV or Mk V.
Colt Official Police or Army Special
During the incident with a telegraph operator Watson draws a different revolver that appears to be a Colt Official Police or, judging by the matte blue finish, a Colt Army Special.
Holmes holds a prop Enfield Mk II revolver on several promotional images. Nevertheless, this gun doesn't appear in the movie itself.
Webley .38 Mk IV Pocket Model
In the scene that depicts Holmes' deduction about the personality of the villain, Mrs. Martha Hudson (Kelly Macdonald) holds a Pocket model of Webley .38 Mk IV revolver with pearl grips (of course, not fitting for 1881 when the story is set). Similar revolver is seen in hands of one of Mrs. Hudson's henchmen, "Charlie Chaplin" (Paul Cassidy).
Inspector Lestrade (Rob Brydon) is seen with a revolver only on the film poster. His revolver is a Webley Metropolitan Police.
Rifles
Lee-Enfield Mk.I
Royal Guards carry rifles that are seen only partially. They are supposed to be Lee-Enfield Mk.I (this model, as like as its direct predecessor Lee-Metford didn't exist in 1881 yet).
Shotguns
Coach Gun
Grace Hart's assistant Millicent (Lauren Lapkus) carries a Coach Gun with exposed hammers.