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Most every model has its own serial # range. That's why Alan's ID link above is so important to identify the model. However very few models that belong in this section of the forum are not marked with the caliber. But for you to post your thread in this section, you must feel confident that it's a Hand Ejector model (swing out cylinder).
In that case if it's a large revolver it could have been a .455 Hand Ejector - 1st or 2nd Model British Svc Revolver made for WWI mostly in Mk II, .455 caliber, but not all. However that # is either not taken from the gun butt and therefore not the serial # or it's in a different model serial # range.
The little .32 Hand Ejector is another unmarked for caliber Hand Ejector, but again that # is not taken from the gun butt and therefore not the serial # or not a.32 HE.
Also when there's no caliber mark on the barrel, or serial # on the butt, they could have been removed! But we can still ID the revolver model with the proper description details.