Can't say specifically, but to buy a 'gun for the continent' meant buying, if one's 'purse' could afford it, "a good gun, in case complete".
That's just the way it was.

If going there, "one MUST be armed appropriately, old chap!"

just a guess

as to the numbers, no idea.
I suspect John Taylor wasn't the only one supporting his "habit" with ivory & horns.

Back in 1861, Forsyth noted, if not wanting the expense of a properly regulated double, "have a good single made instead, along these principals." I suspect having a good single or two, might have been popular and most certainly cheaper than a double and no regulation problems.