I think that Westley Richards would answer your question.

I suspect that the likelihood is that it has been shortened as others have said, but you never know; Westley Richards, like other quality makers would make what the customer wanted.

Slightly puzzled how the last 1/8" has a contraction and comes in comes in at 0.710 because I would have expected the choke in a 30" to be shorter than 2 3/4", but chokes have been made in all sorts of lengths I suppose. Also it may have started life as a 29".