Nothing to add to the combo-gun discussion, but after a lifetime of shooting I recently acquired my first-ever 28-bore shotgun.
Haven't even warmed its barrel yet.

Its one of those gorgeous little top-lever hammer rook rifles that Thomas made for H&H before the turn of the previous century, this one in .425 Rook but bored out to 28ga long ago and reproved in the UK (I presume: 28 in a diamond on the barrel flat).

Oddly, retailed by W.E. Ekins of Adelaide and the locks so-marked. Will toss-up a few photos when I get time.

However, I digress... Apologies!