It gets complicated, Oleg....
Older shotguns are oft chambered for shells shorter than those commonly used these days. The Brits used a 2 inch 12 ga shell, a 2 1/2", a 2 3/4" and even a 3" load for waterfowl guns.
Older 16 gauges are oft chambered for a 2 9/16" shell, and so on.
A modern plastic cased shell of appropriate length, loaded lightly to ease stresses on old shotguns is safe in shotguns that are up to being used.
ALL OLD GUNS SHOULD BE CHECKED OUT BY A COMPETENT SMITH BEFORE FIRING!
NOTE:
When we say a 2 3/4" shell, for example, that means the shell is 2 3/4" or less in the fired state, not as loaded.If the crimp doesn't have enough room to open properly, in the chamber and not abutting into the forcing cone, pressures skyrocket.IOW, using too long a shell can make an old shotgun into a grenade.
Also, some older guns are as tight in the chamber as in the bore, especially European guns. This doesn't matter much unless one is using reloads that haven't been sized.
Otherwise, modern ammo works in old guns PDG.