Why would this be an NFA item?
If the .45/410 barrel is rifled at all, it is still considered a pistol, even if it will fire shot shells, just like the Judge and Govenor revolvers. No NFA forms requiered unless you throw a rifle stock or suppressor on it.
"As we know, there are known knowns. These are things we know that we know. We also know there are known unknowns. That is to say, we know there are some things we do not know. But there are also unknown unknowns, the ones we don't know we don't know."