This is real, and you have to watch how you hold your revolver. It is worse when the cylinder/forcing cone gap is larger, but still a problem even with the closest tolerance. It is worse when you get larger in caliber.
If you’re thinking it’s BS, take a close look at the Circuit Judge Revolver Rifle. They had to put a guard on the cylinder/frame junction to keep users from getting their hands damaged when the user tried to hold the rifle back farther than recommended.
Even worse in front of the cylinder of a black powder revolver, especially if the chambers are filled with grease after loading. A flashback could fire additional chambers. Main reason the Colt revolving rifle was not popular.
Took some debris in the temple a number of years back from a shooter on the line next to me.
I wasn’t in line with the gap either. Always try to wear a good set of curved style shooting classes.
Its also why silencers don’t work very well on revolvers.
Also when shooting with a revolver braced against a barricade, the gases and debris from the cylinder gap can be directed back towards your face.