No idea if it was the first to be loaded from the back...
Nice looking guns that look to be in great shape...
Probably the first official breechloading gun for the swedish army/navy, but not the first breechloader in the whole world since breechloaders or "cannons that can be loaded from the back" we're made since the 1400s.
Because the swedes haven't really fought any wars after 1814, there's never been a serious need to recycle old weapons. That's why there seems to be plenty of antique weapons, cannons including, in great condition in Sweden.
EDIT: The gun is a 23cm M/1854 "Slätborrad Bombkanon", meaning it's a 7" smoothbore shell-gun. There were heavy and light models, but I don't know which is pictured in the photos here. I don't know how the breech works either, but they seem to have fired an odd, a bit oval shaped shell.