You're quite welcome. Glad you enjoyed it. I've wanted one of these things (not specifically a Mk IV, but a WWI-era Very pistol of one kind or another) for years, but never quite got around to it until recently. I like the air of quality it has, and the fact that even as utterly no-frills as it is, it has a bit of style. Back in those days, even the most mundane bits of equipment had a certain—if you'll pardon the expression—flair that tends to be lacking from their modern-day equivalents.

--G.
-><-
Benjamin D. Hutchins, Co-Founder, Editor-in-Chief, & Forum Mod
Eyrie Productions, Unlimited http://www.eyrie-productions.com/
zgryphon at that email service Google has
Ceterum censeo Carthaginem esse delendam.

No, I don't know why the British standard was called that. Maybe it's a one-inch bore but the cartridge is slightly larger? Although why mix measurement systems in that way, I couldn't tell you. (Still more puzzling, by WWII the British were calling that same standard "calibre 4", by which name it is still to be found in marine supply catalogs today.)

--G.
-><-
Benjamin D. Hutchins, Co-Founder, Editor-in-Chief, & Forum Mod
Eyrie Productions, Unlimited http://www.eyrie-productions.com/
zgryphon at that email service Google has
Ceterum censeo Carthaginem esse delendam.

The British, (and thus the Canadians through to about WWII), sometimes use slightly incorrect bore sizes to distinguish between things that are the same size but not compatible.

For example, the 76mm, 3" and 77mm were all actually 76.2mm.

I'm not sure if that's what's happening here, but it is a possibility.

Could be. Or possibly it's an ancient typo in some upstream source, and was originally meant to say 1"/25.4mm. The slash seems to imply that the two values are meant to be different, though, and it's not just a "this is what that is in metric" thing. (shrug) Dunno.

--G.
-><-
Benjamin D. Hutchins, Co-Founder, Editor-in-Chief, & Forum Mod
Eyrie Productions, Unlimited http://www.eyrie-productions.com/
zgryphon at that email service Google has
Ceterum censeo Carthaginem esse delendam.

And, calibre 4 I would think equates to 4-gauge, which is about 26.72mm. What with the mentioned Brit tendency to "eyeball it", as it were...

...!
Stoke Mandeville, Esq & The Victorian Ballsmiths
"Nobody Want Verdigris-Covered Balls!"

Could be, but I suspect that's probably a coincidence; if they had meant to use that system on a non-shotgun, the British convention would've been to call it "4-bore". Calibers are usually given with the number first too, but "4 calibre" would either mean four inches, or four times the bore diameter in length, depending on the context. My guess, though I acknowledge that it is only a guess, is that "calibre 4" just refers to the fourth one on whatever list it appeared on, and that there were other signal cartridge sizes (calibres 1 through 3 and whatever else) that didn't catch on. Similar in concept to the "Rifle № 1" numbering that was retroactively applied to the Mark III SMLE after World War I.

--G.
-><-
Benjamin D. Hutchins, Co-Founder, Editor-in-Chief, & Forum Mod
Eyrie Productions, Unlimited http://www.eyrie-productions.com/
zgryphon at that email service Google has
Ceterum censeo Carthaginem esse delendam.