Hello all,
Just noticed i mispelled the title of the thread! Apologies.
Thank you to all who have posted here with very useful info.
Add two more SXS's with round bolts that I remembered, one is a Belgian Darry with a round bolt measuring 8mm in diameter, fitting in a round recess under the barrels. The other is a Daw circa 1855 (?) with a round bolt which seemed to be around 7 mm in diameter. Both were tight actioned.
From my moderate metalworking experience it would seem that drilling/reaming a round hole is easier than broaching a square recess. I do not know what spark erosion machining has done for this, but even with that technology available the round hole seems easier and perhaps cheaper to make.
