I was surfing and came across these. Probably old news to most people on the list.
http://www.uberti.com/firearms/springfield-trapdoor.php
Good old Uberti! They have a six-groove barrel and unknown twist rate. At the price of the Uberti you can probably pick up a pretty decent trapdoor rifle, and maybe an OK carbine. Just curious as to whether there are any advantages to the replica?
jn