Tim;
I didn't mean it to be snidey. Many, many year ago in elementary school English we were taught there "Are Exceptions to All Rules". I totally agree the vast majority of hammer doubles are Sidelocks but just meant to emphasize there are Exceptions.
Most of the ones I have seen have been in the area of "Hardware" quality guns. I do not off hand know of any double rifles so built, but not able to say positively none were ever made.
Actually at present I have in my custody A hammer double 12 marked New Baker built prior to the move from Syracuse to Batavia which I would call a trigger plate action. J Stevens made some box lock hammer doubles. A cousin of mine has a W H Davenport 12 double which has the hammers coming through the top of the frame rather than on the outside as on the J Stevens.
I do apologize for my post coming across as snide, was just trying to emphasize something I learned a long time ago, be extremely sparing with the use of the words Always or Never. It's best to precede either word with "Almost" because "Almost Allways" there are exceptions.


Miller/TN
I Didn't Say Everything I Said, Yogi Berra