Not to "Bore" anyone here but... The British like to use the term bore for gauge. Something about their national character I suppose.
Now the 410 is properly a bore and not a gauge. The Gauge for 410 is approximately 67.5! Calling it a 67.5 gauge won't do so it is referred to as a 410 bore as it was probably at one time a dangerous game rifle.
British officers were allowed to take one long gun with them when posted to the Empire. And often they took "Paradox" guns. SXS with one rifled barrel and one smoothebore barrel for hunting. Thus the 410 probably came about as a paradox gun and caught on.
The 410 is often marked as a 36 gauge, obviously not an accurate description but easier to pronounce. Some euro guns are still marketed as 36 gauge and some ammo manufacturers might still sell boxes of shells labeled 36 ga....not to be confused with 32 gauge which is a proper gauge and still used in europe.
The Brits calling everything a bore is probably due to the 410 bore, and the British propensity to misspell words.
