SxS, quite often--but not always--British shotshell boxes will provide you with all the information you need, concerning which shells should be fired in which guns. For example, I'm looking at a box of Gamebore Traditional Game shotshells, 28 gram, 2 1/2", 20 gauge. On the box I find:
"WARNING. Please note these cartridges are suitable for use in:
GAME (65/67mm) LOADS: Guns with a chamber length of 2 1/2" (65/67mm) or longer, nitro proofed to a service pressure of 3 tons/sq inch (850 kg/sq cm)."
There's one small glitch in that information, in that 850 kg (or bars) is actually the proof pressure, not the service pressure. But what they're telling you is that those shells can be used in any guns marked either 3 tons or 850 bars. Helpful of them to provide all that information.
